Biodegradable resin foam and method and apparatus for producing same

ABSTRACT

Foam forming techniques are capable of permitting foaming of biodegradable resin to be positively and uniformly accomplished to provide a biodegradable resin foam with satisfactory quality. The biodegradable resin foam is made of biodegradable resin a main biodegradable resin ingredient of 100° C. or more in melting point and a low-melting biodegradable resin ingredient of 100° C. or less in melting point. The biodegradable resin foam is produced by placing a starting material of at least biodegradable resin and a substantial amount of moisture in a heated and pressurized environment, releasing the starting material from the environment to foam the biodegradable resin, and subjecting the foamed resin to forming by a forming mold. An apparatus for producing the foamed biodegradable resin foam includes a pressure adjusting chamber, an air-permeable forming mold, a pressure reducing tank and an injection machine.

This is a divisional application of 08/734,957 filed Oct. 23, 1996, nowU.S. Pat. No. 5,849,339 which is a divisional application of 08/274,038,filed Jul. 12, 1994, now U.S. Pat. No. 5,602,188.

BACKGROUND OF THE INVENTION

This invention relates to biodegradable resin which has been recentlyspotlighted in place of synthetic resin, and more particularly to abiodegradable resin foam obtained by foaming the biodegradable resin anda method and an apparatus for producing the same.

In general, synthetic resin has been applied to a variety of industrialfields because of exhibiting satisfactory mass productivity, moldabilityand durability. In particularly, a synthetic resin foam is light-weightand exhibits increased cushioning properties, to thereby be widely usedin various forms such as a protective casing for a fragile article suchas a glass product, a cushioning material for packing, a tableware, aheat insulation material, a sound insulation material and the like.However, this causes the amount of disposal of such synthetic resinproducts to be extensively increased, leading to various seriousproblems.

More particularly, incineration of synthetic resin causes a large amountof harmful gas to be produced, leading to atmospheric pollution.Disposal of synthetic resin other than the incineration causesenvironmental pollution because it has resistance to oxidation andresistance to decomposition by light and ozone. Also, synthetic resin isextensively increased in intermolecular bond, so that the incinerationcauses generation of much heat, leading to damage to an incinerationfurnace and therefore a decrease in lifetime of the furnace.

In view of the foregoing, much attention has been recently directed tobiodegradable resin and a great effort has been made to developbiodegradable resin.

As a result, processing of biodegradable resin into a film material isnow in the course of being put into practice. Also, development offoaming of biodegradable resin would lead to spread of applicationsthereof, to thereby permit advantages of biodegradable resin to be morewidely exhibited. Techniques of foaming synthetic resin which have beencarried out in the art include a method of producing foamed beadsincluding the steps of charging styrene beads in a forming mold andadding water vapor thereto, followed by a decrease in pressure, a methodof foaming synthetic resin by charging an extruder with, for example,styrene resin together with a foaming agent such as an organic solventor the like to foam the resin due to a pressure reducing actionoccurring when the resin is extruded, and the like.

However, such conventional chemical foaming techniques for foamingsynthetic resin as described above fail to satisfactorily foambiodegradable resin due to a relationship between a softening point ormelting point of the resin and a foaming temperature of a foaming agentand the like. Thus, there are known many problems which are encounteredwith techniques of foaming biodegradable resin to a high degree andforming the foamed resin.

A first problem occurs when a biodegradable resin foam is to be producedby means of, for example, an injection molding machine used forproduction of a conventional synthetic resin foam. More particularly,when biodegradable resin fluidized due to heating and pressurization ina cylinder is extruded through a nozzle of the cylinder into a formingmold, to thereby be decreased in pressure, moisture in the resin isvaporized, leading to expansion. The moisture vaporized is thendecreased in temperature, resulting in suspending in the form of steamin the mold or being condensed on an inner surface of the mold or anouter surface of a molded product. Biodegradable resin generallyexhibits increased hygroscopicity, resulting in being readily softenedand swollen when it is contacted wit moisture. In particular, a film ofeach of foamed cells on an outer portion of a molded or formed productis excessively decreased in thickness, so that it is readily softenedwhen it absorbs condensed water. This results in the foamed cells beingreadily collapsed. Such collapse of the cells is also caused due tore-adhesion of moisture evaporated from the resin to the cells. Thecollapse causes portions of the formed product at which the cells arecollapsed to be shrunk, leading to deformation of the formed product.When the formed product thus deformed is solidified, it is caused to bein a solid form substantially free of any foamed cell. Thus, the formedproduct thus obtained by injection molding fails to exhibit desiredcushioning performance.

A second problem is that the conventional chemical foaming techniquesfail to provide a foamed product having a desired configuration andexhibiting a satisfactory cushioning function. More particularly,foaming of biodegradable resin is started upon release from apressurized state, however, it is highly hard to reach the depths of aforming mold because of exhibiting increased viscosity when it isfluidized by heating. Therefore, foaming of biodegradable resinpartially occurs before the resin extruded from the cylinder reaches thedepths of the forming mold, resulting in a part of the resin which is tobe foamed in the depths of the mold carrying out foaming in the middleof the mold, so that any cavity and/or void are formed in the foamedresin. Such a problem tends to occur in a forming mold of a complicatedconfiguration, Thus, the so-formed biodegradable resin foam is pressedlyforced by biodegradable resin subsequently extruded, so that the portionof the resin which carried out foaming on the way to the depths of themold is crushed by the subsequently extruded resin. Thus, the prior artfails to form the foamed resin into a desired configuration. Also, thefoamed resin fails to exhibit a satisfactory cushioning performance.

A third problem occurs due to releasing of biodegradable resin fluidizedby heating and pressurizing from a heated and pressurized environment.Releasing of the resin fluidized causes moisture contained in the resinto be vaporized and expanded, resulting in foaming of the resin, tothereby provide cells, during which the cells-are decreased intemperature to a level of about 100° C. due to vaporization of themoisture. This causes the cells to be somewhat shrunk and thensolidified while being kept shrunk. Also, the cells are somewhat shrunkby water vapor surrounding the cells. Such cells are integrated togetherto form a foam. Thus, cavities and/or voids occur in the foamsolidified, so that boundaries between the cells are discontinuous, tothereby cause the foam to be unsuitable for use for a cushioningmaterial.

A fourth problem encountered with the conventional chemical foamingtechniques is caused during formation of an pressure reduced atmosphere.More particularly, when a heated and pressurized atmosphere in whichbiodegradable resin is placed is to be changed into a pressure reducedatmosphere, an evacuation or vacuum pump is generally used.Unfortunately, formation of such a pressure reduced atmosphere requiresa considerable period of time, so that a pressure reducing action due tothe change is rendered slow or inactive. Also, this causes moisture tore-adhere to cells while it is not fully exhausted, leading to softeningof the cells, followed by collapse of the cells, resulting in theresultant resin foam being deteriorated in properties or quality. Inorder to prevent such re-adhesion of moisture to the cells, it would beconsidered that formation of the pressure reduced atmosphere is carriedout using a large-sized vacuum pump or the like, resulting in timerequired for evacuation being reduced. However, this causes asignificant increase in manufacturing cost of the foam.

Further, injection of biodegradable resin from a nozzle of a cylinder ofan injection molding machine into a forming mold arranged in a closedatmosphere causes injection resistance to be increased. In order toavoid the problem, it is required to arrange a large-sized injectionmolding machine. Unfortunately, this leads to an increase in cost ofequipment and therefore manufacturing cost. In particular, in order toform a foam with high configuration accuracy, it is required to permitbiodegradable resin to be spread throughout the forming mold. This isadvantageously-accomplished by keeping an atmosphere in the forming moldpressurized during injection molding. However, this causes injectionresistance to be further increased, resulting in the above-describeddisadvantage being rendered amplified.

SUMMARY OF THE INVENTION

The present invention has been made in view of the foregoingdisadvantages of the prior art.

Accordingly, it is an object of the present invention to provide amethod for producing a biodegradable resin foam which is capable ofaccomplishing foaming of biodegradable resin while minimizing orsubstantially preventing shrinkage of formed biodegradable resin due tore-adhesion of moisture thereto, to thereby provide a uniformbiodegradable resin foam.

It is another object of the present invention to provide a method forproducing a biodegradable resin foam which is capable of uniformlyfoaming biodegradable resin.

It is a further object of the present invention to provide a method forproducing a biodegradable resin foam which is capable of minimizing orsubstantially preventing collapse of cells of foamed biodegradable resinto provide a biodegradable resin foam of a desired configuration anduniform quality.

It is still another object of the present invention to provide a methodfor producing a biodegradable resin foam which is capable of providing awater-repellent biodegradable resin foam.

It is yet another object of the present invention to provide a methodfor producing a biodegradable resin foam which is capable of providing abiodegradable resin foam free of any discontinuous boundary betweencells even when any cavity and/or void occurs in biodegradable resinfoamed.

It is even another object of the present invention to provide abiodegradable resin foam which is substantially free of anydiscontinuous boundary between cells even when any cavity and/or voidoccurs in biodegradable resin foamed.

It is a still further object of the present invention to provide anapparatus for producing a biodegradable resin foam which is capable ofpreventing an increase in cost of equipment and accomplishing rapidpressure reduction and evacuation of an atmosphere in a forming mold atan appropriate timing, to thereby provide a biodegradable resin foam ofimproved quality.

It is a yet further object of the present invention to provide anapparatus for producing a biodegradable resin foam which is capable ofpreventing an increase in cost of equipment and facilitating injectionof biodegradable resin into a forming mold while keeping injectionresistance at a minimum level, to thereby increase configurationaccuracy of a biodegradable resin foam.

In accordance with one aspect of the present invention, a biodegradableresin foam is provided which is made of biodegradable resin by expansionforce due to vaporization of moisture caused by rapidly releasingfluidized biodegradable resin which is in a heated and pressurizedenvironment and in which the moisture is trapped. The biodegradableresin may comprise a combination of a first biodegradable resiningredient having a melting point of 100° C. or more or a mainbiodegradable resin ingredient and a second biodegradable resiningredient having a melting point of 100° C. or less or a low-meltingbiodegradable resin ingredient.

In a preferred embodiment of the present invention, the secondbiodegradable resin ingredient may be selected from the group consistingof polycaprolactone and a material containing polycaprolactone.

In a preferred embodiment of the present invention, the biodegradableresin may have a substance selected from the group consisting ofpolyhydric alcohols and derivatives thereof added thereto.

Thus, in the foam of the present invention, the second biodegradableresin ingredient is kept from being immediately solidified, to therebyfunction as an adhesive with respect to the first biodegradable resiningredient. Therefore, even when any cavity and/or void areunfortunately formed in the foamed biodegradable resin, cells of thefoamed resin are permitted to adhere to each other through the secondresin ingredient, resulting in the foam being provided with satisfactoryquality.

When the second biodegradable resin ingredient is selected from thegroup consisting of polycaprolactone and a material containingpolycaprolactone, the function of the second biodegradable resiningredient as an adhesive is substantially enhanced. Also, when thebiodegradable resin has polyhydric alcohols and derivatives thereofadded thereto, moisture in the resin is increased in boiling point,resulting in functioning also as a plasticizer, so that cells of thefoamed biodegradable resin are rendered dense and uniform.

In accordance with another aspect of the present invention, a method forproducing a biodegradable resin foam is provided. The method comprisesthe steps of charging a biodegradable resin starting material containingbiodegradable resin in a cylinder formed at a front portion thereof witha narrowed opening, raising a temperature of the biodegradable resin torender the biodegradable resin fluidized while forcibly transferring thebiodegradable resin starting material toward the narrowed opening in thecylinder, extruding the fluidized biodegradable resin from the cylinderinto an air-permeable forming mold arranged in front of the cylinder torapidly release the biodegradable resin from a heated and pressurizedenvironment in the cylinder to foam the biodegradable resin, and formingthe foamed biodegradable resin into a shape depending on a configurationof the forming mold. Thus, moisture contained in the resin is increasedin boiling point under pressure, resulting in being in the form ofliquid in the cylinder, so that releasing of the resin from the heatedand pressurized environment in the cylinder causes the moisture to beinstantaneously vaporized, leading to foaming of the resin. Theresultant water vapor is outwardly discharged through the air-permeableforming mold, to thereby be prevented from re-adhering to the formedfoam.

In a preferred embodiment of the present invention, an atmosphere inwhich the forming mold is placed is kept decreased in pressure orventilated since a stage before starting of extrusion of the fluidizedbiodegradable resin into the forming mold or since starting of theextrusion. Such construction prevents moisture from remaining in theform of steam in the forming mold or being condensed on a surface of theresin foam due to a decrease in temperature after vaporization andexpansion of the moisture, resulting in the form being provided withsatisfactory uniformity.

In a preferred embodiment of the present invention, the step ofextruding the fluidized biodegradable resin into the mold is carried outwhile placing a nozzle arranged with respect to the narrowed opening inthe depths of the forming mold at the time of starting of the nozzle andretracting the nozzle relative to the forming mold during extrusion ofthe biodegradable resin. This permits the biodegradable resin to becharged in the forming mold in order from the side of the depths of themold, resulting in a difference between a timing at which the resin isspread throughout the forming mold and a timing of foaming of the resinbeing minimized or substantially eliminated, to thereby substantiallyprevent cells of the foamed biodegradable resin from being collapsed.

In a preferred embodiment of the present invention, the step ofextruding the fluidized biodegradable resin into the forming mold iscarried out while keeping an atmosphere in the forming mold pressurizedduring the extrusion and rapidly reducing a pressure of the atmospherein the forming mold after completion of the extrusion. This permits thebiodegradable resin to be foamed while being spread throughout theforming mold, so that the resin foam obtained is formed into a desiredconfiguration.

In a preferred embodiment of the present invention, the step ofextruding the fluidized biodegradable resin into the forming mold iscarried out by injecting the biodegradable resin into the forming moldwhile keeping the resin atomized. This permits not only the resin to bespread throughout the forming mold but the atomized resin to beeffectively foamed, followed by integration of cells of the foamed resinwithout being collapsed, to thereby provide the-resin foam withincreased uniformity.

In a preferred embodiment of the present invention, the biodegradableresin starting material may comprise moisture and the biodegradableresin. Alternatively, it may comprise the biodegradable resin and ahygroscopic fine-particle material having moisture absorbed therein andadded to the biodegradable resin. Also, the biodegradable resin startingmaterial may comprise moisture, the biodegradable resin and a waterrepellent material. The starting material of such composition ensuresdesired foaming of the resin and permits it to be finely and uniformlyfoamed.

Also, the water repellent material may comprise a material which is notfully evaporated when the resin fluidized is released from the heatedand pressurized environment. The material may include a natural fattyacid polymer. Use of the polymer as the water repellent material permitsit to cover cells of the foamed resin to provide it with water repellentproperties, to thereby prevent the cells from being collapsed due tocontact with water.

In a preferred embodiment of the present invention, the step of formingthe foamed biodegradable resin into a shape depending on a configurationof the forming mold may be carried out by forming the wholebiodegradable resin into an integrated configuration. This permits theresin foam to be formed into a relative large volume or any desiredconfiguration.

In a preferred embodiment of the present invention, the biodegradableresin comprises a first biodegradable resin ingredient having a meltingpoint of 100° C. or more and a second biodegradable resin ingredienthaving a melting point of 100° C. or less.

In a preferred embodiment of the present invention, the secondbiodegradable resin ingredient is selected from the group consisting ofpolycaprolactone and a material containing it.

In a preferred embodiment of the present invention, the biodegradableresin has a substance selected from the group consisting of polyhydricalcohols and derivatives thereof added thereto.

In accordance-with a further aspect of the present invention, anapparatus for producing a biodegradable resin foam is provided. Theapparatus comprises a pressure adjusting chamber constructed in a mannerto be capable of being opened and closed hermetically, an air-permeableforming mold arranged in the pressure adjusting chamber, a pressurereducing tank connected to the pressure adjusting chamber to rapidlyreduce a pressure in the pressure adjusting chamber, and an injectionmachine for injecting, into the forming mold, fluidized biodegradableresin placed in a heated and pressurized environment and having moisturetrapped therein. Thus, the apparatus permits the pressure reducing tankto communicate with the pressure adjusting chamber after injection ofthe resin into the forming mold, so that water vapor produced in theforming mold may be effectively outwardly discharged, to therebyeliminate retention of moisture in the forming mold. Thus, thebiodegradable resin foam product obtained is provided with a desiredconfiguration and uniform quality.

In a preferred embodiment of the present invention, the pressureadjusting chamber has an evacuation valve connected thereto. Thus, whenthe pressure adjusting chamber is rendered open to an ambient atmospherein the course of injection of the rein into the forming mold, resistanceto the injection is reduced because the forming mold is air-permeable,so that the injection may be facilitated. Therefore, the injectionmachine is prevented from being large-sized.

In a preferred embodiment of the present invention, the pressureadjusting chamber has a compressor connected thereto. This permitsinjection of the resin into the forming mold to be carried out whilekeeping moisture positively trapped in the resin because actuation ofthe compressor pressurizes the pressure adjusting chamber. Then,operation of the evacuation valve results in the pressure adjustingchamber being released from pressurization, leading to a decrease ininjection resistance, so that the resin may be spread throughout theforming mold.

In a preferred embodiment of the present invention, the pressureadjusting chamber has a pressurizing tank connected thereto. Thispermits the pressure adjusting chamber to be rapidly pressurized at anappropriate timing when the resin is to be injected into the formingmold.

Also, in accordance with this aspect of the present invention, anapparatus for producing a biodegradable resin foam is provided. Theapparatus comprises a pressure adjusting chamber constructed in a mannerto be capable of being opened and closed hermetically, an air-permeableforming mold arraged in the pressure adjusting chamber, a pressurereducing tank connected through a pressure reducing valve to thepressure adjusting chamber to rapidly reduce a pressure in the pressureadjusting chamber, an evacuation valve connected to the pressureadjusting chamber, a compressor connected to the pressure adjustingchamber, a valve controller for controlling operation of each of thevalves, and an injection machine for injecting, into the forming mold,fluidized biodegradable resin placed in a heated and pressurizedenvironment and having moisture trapped therein. The valve controllerfunctions to initiate actuation of the compressor before or at the timewhen injection of the biodegradable resin into the forming mold by theinjection machine is started, carry out termination of actuation of thecompressor and opening of the evacuation valve in the course of theinjection, and carry out closing of the evacuation valve and opening ofthe pressure reducing valve after the injection. Thus, the pressureadjusting chamber may be controlled to pressurization, evacuation orpressure reduction in association with a timing of injection of theresin into the forming mold.

Further, in accordance with this aspect of the present invention, anapparatus for producing a biodegradable resin foam is provided. Theapparatus comprises a pressure adjusting chamber constructed in a mannerto be capable of being opened and closed hermetically, an air-permeableforming mold arranged in the pressure adjusting chamber, a pressurereducing tank connected through a pressure reducing valve to thepressure adjusting chamber to rapidly reduce a pressure in the pressureadjusting chamber, an evacuation valve connected to the pressureadjusting chamber, a pressurizing tank connected through a pressurizingvalve to the pressure adjusting chamber, a valve controller forcontrolling operation of each of the valves, and an injection machinefor injecting, into the forming molds fluidized biodegradable resinplaced in a heated and pressurized environment and having moisturetrapped therein. The valve controller functions to open the pressurizingvalve before or at the time when injection of the biodegradable resininto the forming mold by the injection machine is started, carry outclosing of the pressurizing valve and opening of the evacuation valve inthe course of the injection, and carry out closing of the evacuationvalve and opening of the pressure reducing valve after the injection.Thus, the pressure adjusting chamber is controlled to pressurization,evacuation or pressure reduction in association with a timing of theinjection.

In addition, in accordance with this aspect of the present invention, anapparatus for producing a biodegradable resin foam is provided. Theapparatus comprises a pressure adjusting chamber constructed in a mannerto be capable of being opened and closed hermetically, an air-permeableforming mold arranged in the pressure adjusting chamber, a pressurereducing tank connected through a pressure reducing valve to thepressure adjusting chamber to rapidly reduce a pressure in the pressureadjusting chamber, an evacuation valve connected to the pressureadjusting chamber, a valve controller for controlling operation of eachof the valves, and an injection machine for injecting, into the formingmold, fluidized biodegradable resin placed in a heated and pressurizedenvironment and having moisture trapped therein. The valve controllerfunctions to open the evacuation valve in the course of injection of thebiodegradable resin into the forming mold by the injection machine andcarry out closing of the evacuation valve and opening of the pressurereducing valve after the injection. Thus, the pressure adjusting chamberis controlled to evacuation or pressure reduction in association with atiming of the injection.

Furthermore, in accordance with this aspect of the present invention, anapparatus for producing a biodegradable resin foam is provided. Theapparatus comprises a pressure adjusting chamber constructed in a mannerto be capable of being opened and closed hermetically, an air-permeableforming mold arranged in the pressure adjusting chamber, a pressurereducing tank connected through a pressure reducing valve to thepressure adjusting chamber to rapidly reduce a pressure in the pressureadjusting chamber, a pressurizing tank connected through a pressurizingvalve to the pressure adjusting chamber, a valve controller forcontrolling operation of each of said valves, and an injection machinefor injecting, into the forming mold, fluidized biodegradable resinplaced in a heated and pressurized environment and having moisturetrapped therein. The valve controller functions to open the pressurizingvalve before or at the time when injection of the biodegradable resininto the forming mold by the injection machine is started and carry outclosing of the pressurizing valve and opening of the evacuation valveafter the injection. This permits the pressure adjusting chamber to becontrolled to pressurization or pressure reduction in association with atiming of the injection.

In a preferred embodiment of the present invention, the injectionmachine includes a cylinder having a narrowed opening formed at a frontportion thereof, a forcible transfer mechanism for forcibly transferringa biodegradable resin starting material containing biodegradable resinand charged in the cylinder and raising a temperature of thebiodegradable resin, to thereby fluidize it and extruding the fluidizedbiodegradable resin through the narrowed opening into a forming mold,and an access mechanism for reciprocating the narrowed opening andforming mold relative to each other and retracting the narrowed openingrelative to the forming mold during injection of the fluidizedbiodegradable resin through the narrowed opening into the forming mold.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and many of the attendant advantages of thepresent invention will be readily appreciated as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings; wherein:

FIG. 1 is a vertical sectional side elevation view generally showing anexample of an apparatus suitable for use for practicing an embodiment ofa method for producing a biodegradable resin foam according to thepresent invention;

FIGS. 2(a) to 2(c) each are a schematic sectional view showing each ofsteps of the method of FIG. 1;

FIG. 3 is a perspective view showing an embodiment of a biodegradableresin foam according to the present invention;

FIG. 4 is a vertical sectional side elevation view showing an essentialpart of another example of the apparatus suitable for use for practicingthe method of FIG. 1;

FIG. 5 is a vertical sectional side elevation view showing an essentialpart of a further example of the apparatus suitable for use forpracticing the method of FIG. 1;

FIG. 6 is a vertical sectional side elevation view generally showing anexample of an apparatus suitable for use for practicing anotherembodiment of a method for producing a biodegradable resin foamaccording to the present invention;

FIGS. 7(a) to 7(c) each are a schematic sectional view showing each ofsteps of the method of FIG. 6;

FIG. 8 is a vertical sectional side elevation view showing an essentialpart of another example of the apparatus suitable for use for practicingthe method shown in FIG. 6;

FIG. 9 is a vertical sectional side elevation view generally showing anexample of an apparatus suitable for use for practicing a furtherembodiment of a method for producing a biodegradable resin foamaccording to the present invention;

FIGS. 10(a) to 10(c) each are a schematic sectional view showing each ofsteps of the method of FIG. 9;

FIG. 11 is a vertical sectional side elevation view showing an essentialpart of a further example of the apparatus suitable for use forpracticing the method shown in FIG. 9;

FIG. 12 is a vertical sectional side elevation view generally showing anexample of an apparatus suitable for use for practicing still anotherembodiment of a method for producing a biodegradable resin foamaccording to the present invention;

FIGS. 13(a) to 13(c) each are a schematic sectional view showing each ofsteps of the method of FIG. 12;

FIG. 14 is a perspective view showing a modification of a nozzlearranged with respect to a narrowed opening;

FIG. 15 is a perspective view showing a cylinder provided at a distalend thereof with a shower;

FIG. 16 is a vertical sectional side elevation view showing an essentialpart of another example of the apparatus suitable for use for practicingthe method of FIG. 12;

FIG. 17 is a vertical sectional side elevation view generally showing anexample of an apparatus suitable for use for practicing yet anotherembodiment of a method for producing a biodegradable resin foamaccording to the present invention;

FIGS. 18(a) and 18(b) each are a schematic sectional view showing eachof steps of the method of FIG. 17;

FIG. 19 is a perspective view showing another embodiment of abiodegradable resin foam according to the present invention;

FIG. 20 is a vertical sectional side elevation view showing an essentialpart of another example of the apparatus suitable for use for practicingthe method of FIG. 19;

FIG. 21 is a vertical sectional side elevation view generally showing anembodiment of an apparatus for producing a biodegradable resin foamaccording to the present invention;

FIG. 22 is a side elevation view showing an essential part of anotherembodiment of an apparatus for producing a biodegradable resin foamaccording to the present invention;

FIG. 23 is a timing chart showing a timing of each of injection,evacuation and pressure reduction in operation of the apparatus of FIG.22;

FIG. 24 is a side elevation view showing an essential part of a furtherembodiment of an apparatus for producing a biodegradable resin foamaccording to the present invention;

FIG. 25 is a side elevation view showing an essential part of stillanother embodiment of an apparatus for producing a biodegradable resinfoam according to the present invention;

FIG. 26 is a timing chart showing a timing of each of injection,evacuation and pressure reduction in operation of the apparatus of FIG.25;

FIG. 27 is a side elevation view showing an essential part of yetanother embodiment of an apparatus for producing a biodegradable resinfoam according to the present invention;

FIG. 28 is a side elevation view showing an essential part of evenanother embodiment of an apparatus for producing a biodegradable resinfoam according to the present invention;

FIG. 29 is a side elevation view showing an essential part of a stillfurther embodiment of an apparatus for producing a biodegradable resinfoam according to the present invention;

FIG. 30 is a side elevation view showing an essential part of a yetfurther embodiment of an apparatus for producing a biodegradable resinfoam according to the present invention;

FIG. 31 is a vertical sectional side elevation view showing an essentialpart of a yet further embodiment of an apparatus for producing abiodegradable resin foam according to the present invention;

FIG. 32 is a vertical sectional side elevation view showing an essentialpart of an even further embodiment of an apparatus for producing abiodegradable resin foam according to the present invention;

FIG. 33 is a vertical sectional side elevation view showing an essentialpart of an additional embodiment of an apparatus for producing abiodegradable resin foam according to the present invention; and

FIGS. 34 to 36 each are a vertical sectional side elevation view showinganother embodiment of an apparatus for producing a biodegradable resinfoam according to the present invention which is constructed so as topermit a pressure in an atmosphere in a space of a forming mold to bereduced and permits such pressure reduction to be accomplished in alarge scale.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, the present invention will be described hereinafter with referenceto the accompanying drawings.

The following description of the present invention will be made first ona biodegradable resin foam according to the present invention and thenon a method for producing a biodegradable resin foam together with anapparatus therefor. Then, an apparatus for producing a biodegradableresin foam featured in a mechanism for adjusting a pressure in a formingmold and a method for producing a biodegradable resin foam practicedusing the apparatus will be described. Further, an apparatus and amethod for producing a biodegradable resin foam each of which isconstructed so as to permit a volume in a forming space to be varied asdesired will be described.

The present invention is directed to a biodegradable resin foam, whichis generally designated at reference character B in FIGS. 2 and 3. Thebiodegradable resin foam B is produced by foaming biodegradable resin bymeans of expansion force due to vaporization of moisture. Thebiodegradable resin consists of a first biodegradable resin ingredientof 100° C. or more in melting point (hereinafter also referred to as“main biodegradable resin ingredient”) and a second biodegradable resiningredient of 100° C. or less in melting point (hereinafter alsoreferred to as “low-melting biodegradable resin ingredient”).

The term “biodegradable resin” used herein indicates a resin materialwhich is decreased in physical properties due to a biological action andsuch biodegradable resin includes resin of the type that it per se isfully decomposed and resin of the type that it is blended with resinhard to be decomposed, resulting in it being provided with degradativeproperties. The resin of the former type includes products by microbes,products of natural high-molecular substances, products of petroleummaterials and the like and that of the latter type includes blends withstarch, blends with aliphatic polyesters and the like. Biodegradation ofthe biodegradable resin includes biodegradation by an enzyme such aslipase, amylase, cellulase, protease or the like, that by microbes inactive sludge or the like, that by soil in a natural environment such asforest or cultivated land, and the like.

More particularly, the biodegradable resin includes polyhydroxy butyricacid and derivatives thereof, pullulan, a cellulose-chitosan mixture, anester compound of cellulose, amylose or wood meal, a polyester-nyloncopolymer, and a blend of starch and polyethylene, as well as polyvinylalcohol, polyether, polyurethane, polyamide and the like. Such materialssubstantially have a low-melting point and are readily decomposed in thepresence of water.

The first biodegradable resin ingredient of 100° C. or more or mainbiodegradable resin ingredient which is commercially available includesresin sold under “Mater-Bi” (registered trademark) from Nippon, GoseiKagaku Kabushiki Kaisha, Japan. The resin was developed by Novamontbelonging to a Montedison group, Italy and is said to be a thermoplasticbiodegradable polymer comprising derivatives from a plurality ofagricultural products such as starch and the like and denaturedpolyvinyl alcohol wherein the derivatives and alcohol get into eachother at a molecular level, to thereby bonded to each other by hydrogenbonding. Also, it is said that the biodegradable resin is swollen due toabsorption of moisture, resulting in biodegradation thereof beingpromoted, to thereby exhibit substantially the same biodegradability aspaper in an environment in which microbes exist. In addition to“Mater-Bi” described above, for example, acetate which is an estercompound of cellulose may be of course used as the first biodegradableresin ingredient having a melting point of 100° C. or more. In thisinstance, the biodegradable resin may comprise only the firstbiodegradable resin ingredient of 100° C. or less in melting point ormain biodegradable resin ingredient, to thereby eliminate addition ofthe second biodegradable ingredient of 100° C. or less in melting pointor low-melting biodegradable resin ingredient described hereinafterthereto.

The low-melting biodegradable resin ingredient, even when any cavity orvoid occurs in the biodegradable resin during formation of thebiodegradable resin into a foam, functions to permit walls of cells ofthe foam to adhere to each other as much as possible. In the presentinvention, for example, polycaprolactone or a material containingpolycaprolactone may be preferably used for the low-meltingbiodegradable resin ingredient. Such a low-melting biodegradable resiningredient which may be commercially available includes resin sold undera tradename “Tone” from Nippon Unicar Kabushiki Kaisha, Japan. Thecommercially available resin “Tone” comprises polycprolactone which isaliphatic polyester chemically synthesized and is of the fulldecomposition type.

Also, in the present invention, the biodegradable resin may havepolyhydric alcohols and/or derivatives thereof added thereto as desired.In particular, glycols are preferably added to the resin. Addition ofpolyhydric alcohols or the derivatives permits moisture in thebiodegradable resin to be increased in boiling point, so that themoisture functions also as a plasticizer. Also, the polyhydric alcoholsand the derivatives per se each also act as a plasticizer, so that thecells of the foamed biodegradable resin may be rendered compact anduniform. The polyhydric alcohols and derivatives include glycerin,polyethylene glycol and the like, and derivatives thereof.

A means for permitting moisture to be contained or present in thebiodegradable resin is not limited to any specific means. For example, asuitable amount of moisture may be previously contained in the resinwhen pellets of the biodegradable resin for foaming are formed.Alternatively, a pretreatment step is provided for permitting a suitableamount of moisture to be positively contained in particles of the resin.Alternatively, moisture may be charged in a hopper together withbiodegradable resin directly or through a kneader. Thus, it will benoted that feeding of the biodegradable resin and moisture is notlimited to any specific manner. Also, addition of a fine particle-likehygroscopic material having moisture previously absorbed therein suchas, for example, talc or silica to the biodegradable resin as-in thepellets for foaming permits a foam having cells formed finely anduniformly to be provided, because moisture in the fine particlesexhibits good compatibility and dispersion with respect to thebiodegradable resin as compared with moisture directly added thereto andmoisture in the fine particles contributes to foaming of the resin whileoriginating from the fine particles.

The biodegradable resin foam B of the present invention is produced byfoaming the biodegradable resin kept fluidized by heating and pressuringby means of expansion force due to vaporization of moisture containedtherein. At this time, the resultant foamed resin is reduced intemperature to a level of about 100° C. by vaporization of the moisture.This causes the main biodegradable resin ingredient or firstbiodegradable resin ingredient to be solidified because a melting pointthereof is 100° C. or more, whereas the low-melting biodegradable resiningredient or second biodegradable resin ingredient is kept from beingsolidified because its melting point is 100° C. or less; so that thelatter ingredient acts as an adhesive with respect to the formeringredient. Thus, even when any cavity and/or void occur in the foamedresin during the formation, walls between cells of the foamed resin aresubstantially adhered to each other, so that the biodegradable resinfoam B may be provided with satisfactory quality.

When the biodegradable resin starting material for the biodegradableresin foam B of the present invention comprises moisture, thebiodegradable resin and a water repellent material, the water repellentmaterial and moisture may be previously contained in or added to thebiodegradable resin, followed by charging the starting material into aninjection molding machine, because the biodegradable resin is placedunder a heating and pressurizing condition in the presence of the waterrepellent material and substantial moisture. The water repellentmaterial may include silicone compounds, fluorine compounds, waxes,polymers of a higher fatty acid and the like. In the illustratedembodiment, a commercially available material which is manufactured byKabushiki Kaisha Sigma Gijutu Kenkyujo and sold from Tonen KabushikiKaisha under a tradename “Sigma coat” and mainly consists of polymers ofa higher aliphatic acid and waxes may be used as the water repellentmaterial. Addition of the water repellent material to the biodegradableresin-may be carried out, for example, by diluting the water repellentmaterial (“Sigma Coat”) with water and then heating it to form anemulsion, followed by addition of the emulsion thereto. This permits thewater repellent material and moisture to be concurrently added to thebiodegradable resin. Alternatively, addition of the water repellentmaterial to the biodegradable material and that of moisture thereto maybe carried out separately from each other. For this purpose, the waterrepellent material may be added to the biodegradable resin containingmoisture. The biodegradable resin foam B of the present invention thusformed is not limited to an application to a cushioning material. It maybe directed to various applications such as a heat insulating material,a sound insulating material and the like as in a conventional foamedstyrol material.

Now, a method for producing a biodegradable resin foam according to thepresent invention will be described hereinafter together with anapparatus suitable for use for practicing the method. First, theapparatus will be described with reference to FIG. 1.

The apparatus includes a cylinder 1 formed into a shape like acylindrical container, which is provided on an upper portion of a rearend section thereof with a hopper 11 for charging a biodegradable resinstarting material for a resin foam therethrough into the cylinder 1. Thecylinder 1 is formed at a distal end thereof with a narrowed opening 1 aand provided on around a periphery thereof with a heater 13.

The cylinder 1 is provided therein with a screw 2 in a manner to extendin a longitudinal direction thereof and be in proximity to an innersurface thereof. The screw 2 is so arranged that a rear end thereof isoutwardly projected through an opening formed at a rear end of thecylinder 1 and connected to a front portion of a hydraulic motor 21 forrotating the screw 2. The hydraulic motor 21 is mounted on a rearportion thereof with a piston 23, which is slidably received in aninjection cylinder 22, so that the piston 23, hydraulic motor 21 andscrew 2 are hydraulically moved integrally with each other in thelongitudinal direction of the cylinder 1 and the screw 2 is rotated bythe hydraulic motor 21.

Thus, an injection machine S which is a so-called in-line screw typeinjection molding machine is constructed. The injection apparatus S isprovided at a distal end section thereof with an air-permeable formingmold A, which includes a fixed mold part 3 formed with a cavity 31communicating with the narrowed opening 1 a of the cylinder 1 and amovable mold part 4 formed with a core 41. In the illustratedembodiment, the cavity 31 is formed into a configuration like asubstantially triangular pyramid and the core 41 is formed into atriangular pyramid-like shape corresponding to the cavity 31 but smallerby a thickness of a formed product or resin foam B (FIG. 3) than thecavity 31. The fixed and movable mold parts 3 and 4 thus constructed areclamped together, to thereby define a space of a trihedral structure ofwhich three surfaces are perpendicular to each other, resulting inproviding such a formed product or biodegradable resin foam productshown in FIG. 3.

Reference numeral 40 designates a mold clamp mechanism arranged incombination with the forming mold A, which mechanism includes tie bars42 and 43, and an actuator mechanism 44 for accessibly operating the tiebars 42 and 43 and movable mold part 4 so as to access the movable moldpart 4 to the fixed mold part 3 while keeping both parts opposite toeach other.

The forming mold A is made of a porous material having a number of poresor holes formed therein while being arranged in a net-like manner so asto communicate an interior of the mold A with an exterior thereof. Sucha porous material includes a foamed metal material, a sintered materialmade by sintering metal, ceramic or the like to which a filler capableof forming the material with voids is added, a material made bysubjecting a wire mesh, a punched metal plate or the like to pressingand laminating, and the like. The forming mold A may be readily made,for example, by forming a single punched metal plate into apredetermined configuration. In this case, an increase in size of poresof the porous material leads to an increase in efficiency of exhaust ofwater vapor and efficiency of ventilation, however, an excessiveincrease in size of the pores causes roughness due to the pores toappear on a surface of the foamed resin after foaming of the resin.Thus, the pores of the porous material should be set to a size whichpermits a surface of the resin foam to be provided with smoothnesssuitable for applications to which the foam is directed while preventingresistance to permeation of air through the mold A from beingexcessively increased. In view of the above, a punched metal plate issuitable for use as the porous material for the forming mold A becauseit permits a diameter of the pores, the number thereof and a pitchthereof and the like to be readily set and is simplified in structure.

The forming mold A and mold clamp mechanism 40 are arranged in a chamber5 of an airtight structure acting as a pressure adjusting chamber. Thechamber 5 includes a wall joined to a rear surface of the fixed moldpart 3 of the mold A and is provided with a door (not shown) throughwhich the resin foam made of biodegradable resin is removed. The chamber5 has a pressure reducing pipe L₁ connected thereto, which is providedwith a pressure reducing valve V₁ and connected to a pressure reducingpump P₁ through the valve V₁. Also, the chamber 5 has an atmosphericpressure releasing pipe L₀ connected thereto, which is provided with anatmospheric pressure releasing valve V₀ for releasing pressure in thechamber from a reduced pressure state to an atmospheric pressure.

Now, a method for producing a biodegradable resin foam according to thepresent invention practiced using the apparatus constructed as describedabove will be described hereinafter.

First, the forming mold A is clamped through the mold clamp mechanism 40and-the pressure reducing valve V₁ is closed to keep the chamber 5 at anatmospheric pressure. Then, as shown in FIG. 1, the hopper 11 is fedwith biodegradable resin particles 10 in which moisture is contained,which are then forcedly forwardly transferred in the cylinder 1 by meansof the screw 2. The biodegradable resin particles 10 are increased intemperature to a level of a softening point of the resin or meltingpoint thereof by shearing force due to rotation of the screw 2 andheating applied thereto from the heater 13, resulting in being fluidizedin an inner space of the cylinder 1 defined on a distal end side of thescrew 2.

At this time, the inner-space of the cylinder 1 is kept heated andpressurized, so that moisture contained in the biodegradable resinparticles 10 is kept trapped in the fluidized biodegradable resinwithout evaporating therefrom. Then, rotation of the screw 2 is stoppedand then the piston 23 in the injection cylinder 22 is actuated toforwardly move the screw as shown in FIG. 2(a), resulting in thefluidized biodegradable resin being injected through the narrowedopening 1 a into a forming space R defined in the forming mold A at astretch.

This causes the biodegradable resin in the heated and pressurized stateto be rapidly exposed to atmospheric pressure, so that moisture trappedtherein may be instantaneously vaporized, leading to foaming of theresin. Vaporization of the moisture causes expansion forces to occur inthe biodegradable resin. However, an outermost portion of the resin iscontacted with an inner surface of the forming mold A, resulting inbeing regulated by a configuration of each of the cavity 31 and core 41,to thereby provide a biodegradable resin foam product B as shown in FIG.3 which is wholly integrally formed.

In the foaming, the moisture is decreased in temperature after thevaporization and expansion, resulting in drifting inside and outside theforming mold A in a steam state or condensing on a surface of each ofthe forming mold A and foam product due to contact therewith, so thatthe moisture tends to form water droplets. In order to avoid formationof water droplets, the pressure-reducing valve V₁ is open immediatelyafter extrusion of the biodegradable resin into the forming mold A asshown in FIG. 2(b), to thereby reduce a pressure in the chamber 5 to agauge pressure of, for example, about 750 mmHg by evacuation through thepressure reducing pump P₁. During the evacuation, water vapor ispartially sucked in the pressure reducing pipe L₁ prior to formation ofwater droplets. Also, moisture which tends to form water droplets on thesurface of each of the forming mold A and resin form product B due tocondensation is likewise removed by evacuation under a reduced pressure.

Following evacuation under a reduced pressure for a predetermined periodof time, the pressure reducing valve V₁ is closed and the atmosphericpressure releasing valve V₀ is open, so that air is introduced throughthe atmospheric pressure releasing pipe L₀ into the chamber 5 to returnthe chamber to an atmospheric pressure. Then, the screw 2 is retractedwhile being rotated as shown in FIG. 2(c), resulting in the nextbiodegradable resin fluidized starting to collect in the inner space ofthe cylinder 1 on the side of the distal end of the screw 2 for the nextinjection, during which cooling and solidification of the biodegradableresin foam product B in the forming space R of the forming mold A iscompleted. Thereafter, the forming mold A is rendered open to remove theformed biodegradable resin form product B therefrom, followed by beingclamped for the next operation.

The forming mold A, as described above, is formed at at least a partthereof of a porous material which permits an exterior of the mold A andan interior thereof to communicate with each other, to thereby beprovided with air-permeability, resulting in a pressure of gas generatedin the forming mold A due to expansion of moisture being effectivelyescaped to the exterior of the mold A. This not only effectivelyprevents the gas pressure from collapsing the resultant biodegradableresin foam, but decreases a pressure in the chamber 5 due to evacuationto forcibly remove moisture contributing foaming of the resin from thechamber 5, to thereby keep the resin foam from being contacted with themoisture. Thus, cells of the resin foam are substantially prevented frombeing collapsed, resulting in satisfactory cells being uniformlydistributed over the resultant resin foam, so that it may be effectivelyused as a uniform cushioning material.

Alternatively, the illustrated embodiment may be constructed in such amanner that moisture is previously absorbed in a hygroscopicfine-particle material, which is then dispersed in the biodegradableresin, to thereby provide the biodegradable resin starting material forthe resin foam. In this instance, the moisture is highly uniformlydispersed in the biodegradable resin fluidized which is extruded fromthe injection machine S while being kept carried on the fine particles,so that the moisture permits the resin to be foamed while acting thefine particles as an origin or center of the foaming, resulting infoaming of the resin being rendered uniform.

The apparatus suitable for use for practicing the method of the presentinvention may be constructed as shown in FIG. 4. More particularly, anapparatus shown in FIG. 4 includes a chamber 5 divided into amovable-side part 51 and a fixed-side part 52, wherein the movable-sidepart 51 is arranged so as to be movable together with the movable moldpart 4. Such construction permits the forming mold A and chamber 5 to beconcurrently operated, to thereby facilitate removal of thebiodegradable resin foam B from the mold A and chamber 5.

Now, an experiment made for ascertaining functions and advantages of thepresent invention will be described hereinafter.

Experiment

Biodegradable resin foams were produced while varying a period of timebetween starting of extrusion of the biodegradable resin through thenarrowed opening 1 a and starting of evacuation under a reduced pressure(release lapse time) and a period of time during which evacuation wascarried out (pressure reduction time), followed by observation of theproducts.

Conditions for Experiment

An injection molding machine of Type PS60E12ASE manufactured by NisseiJushi Kogyo Kabushiki Kaisha, Japan was used as the injection machine S.The injection molding machine had a screw diameter of 36 mm, aninjection rate of 12.3 cm/sec, an injection pressure of 1825 kgf/cm², ascrew rotation speed of 0 to 190 rpm at high torque and 0 to 250 rpm atlow torque, and a back pressure of 60 kgf/cm². The experiment was madeunder injected conditions that the injection rate, injection pressure,screw rotation speed, back pressure and variable are set to be 98%, 98%,90%, 30% and 40 mm, respectively.

The forming mold A used was constructed by forming a punched metalwholly formed with holes of about 1.2 mm in diameter and having athickness of 1.5 mm into a box-like shape (100 mm×100 mm×50 mm) bywelding and the like. The chamber 5 was formed into a volume 50 l insuch a manner as shown in FIG. 4 and evacuated to a gauge pressure of750 mmHg.

Results of Experiment

The results were as shown in Table 1.

TABLE 1 Release Lapse Pressure Reduction Volume Density Time (sec) Time(sec) (cc) (g/cc) State 0 5 635 0.041 Δ 5 0 454 0.050 x 5 10 504 0.046 ∘5 20 502 0.046 ∘ 5 30 526 0.043 ∘ 5 120 531 0.043 ∘ 1 30 608 0.042 ⊚

In Table 1, X indicates that the resin foam exhibited remarkableshrinkage, Δ indicates that the resin foam was formed with a lot ofvoids, ◯ indicates that the foam was decreased in shrinkage, and ⊚indicates that the foam was substantially free of shrinkage. Thepressure reduction time “0” indicates that the chamber 5 was kept frombeing evacuated for pressure reduction, resulting in being kept at anatmospheric pressure. As will be noted from the results-shown in Table1, evacuation for pressure reduction permits shrinkage of thebiodegradable resin to be decreased.

In the illustrated embodiment, a timing of evacuation for pressurereduction in the chamber 5 may be set before, during or after extrusionof the biodegradable resin via the narrowed opening 1 a into the formingmold A. Alternatively, the above-described pressure reduction due toevacuation of an atmosphere surrounding the forming mold A may bereplaced with a means shown in FIG. 5. More particularly, the formingmold A is located in a ventilating duct D having a fan f arrangedtherein, so that moisture may be removed from an interior of the formingmold A by actuation of the fan f, to thereby keep the resin foam frombeing contacted with the moisture.

Although narrowed opening 1 a is kept open and the hopper 11 of thecylinder 1 is also kept open, the cylinder 1 is kept closed to a certaindegree, However, a decrease in degree of closing of the cylinder 1causes pressurization in the cylinder 1 to be insufficient, so thatthere is a possibility that a relationship between a softening point ormelting point of the biodegradable resin and a boiling point of moistureor water pressurized in the cylinder causes the moisture to be partiallyvaporized, resulting in foaming of the biodegradable resin occurring inthe cylinder 1 prior to injection of the resin into the forming mold.Also, this tends to cause foaming of the biodegradable resin extrudedfrom the narrowed opening 1 a while causing it to hang down from thenarrowed opening 1 a. In order to avoid such a problem, it is preferablethat the illustrated embodiment is provided with a means for increasinga degree of closing of the cylinder 1. For this purpose, the narrowedopening 1 a may be provided with a nozzle equipped with a shut-offvalve. Alternatively, the hopper 11 for feeding the starting material tothe cylinder 1 may be constructed so as to be tightly closed. Also, thehopper may be provided with a rotary valve. Further, foaming of thebiodegradable resin in the cylinder 1 prior to the injection may berestrained by dissolving a non-volatile solute such as polyethyleneglycol in water and then adding the resultant solution to thebiodegradable resin to increase a boiling point of water.

When the hygroscopic fine particles described above is added to thebiodegradable resin, production of the biodegradable resin foam B is notlimited to extrusion of the biodegradable resin from the injectionmolding machine or injection machine S into the forming mold A. It maybe carried out in such a manner that the forming mold A in which thebiodegradable resin having the hygroscopic fine-particle materialpreviously dispersed therein is charged is arranged in a closed heatingvessel and then the heating vessel is fed with heated water vapor,followed by a rapid decrease in pressure in the heating vessel. Thehygroscopic fine-particle material is not limited to a round powderyconfiguration. It may be formed into a shape like a thin piece or arod-like shape.

In the illustrated embodiment, it is not necessarily required to add thehygroscopic fine-particle material to the biodegradable resin. Thebiodegradable resin may have water previously contained therein.Alternatively, biodegradable resin containing equilibrium moisture underan atmospheric pressure may be used for the present invention. Also, thebiodegradable resin and moisture or water may be separately added to thehopper 1.

In the illustrated embodiment, extrusion of the fluidized biodegradableresin into the forming mold may be carried out while placing a nozzlearranged with respect to the narrowed opening in the depths of theforming mold at the time when operation of the nozzle is started andretracting the nozzle relative to the forming mold during extrusion ofthe biodegradable resin. This may be carried out by means of anapparatus constructed in such a manner as shown in FIG. 6.

The apparatus shown in FIG. 6 includes an elongated nozzle 16 connectedto a narrowed opening 1 a so as to forwardly outwardly extend in alongitudinal direction of a cylinder 1. In correspondence to arrangementof the nozzle 16, a heater 13 may be arranged in the nozzle 12 as wellas around the cylinder 1. Also, a fixed mold part 3 of a forming mold Ais formed with a through-hole 32 communicating with a cavity 31, so thatthe nozzle 12 may be inserted into the fixed mold part 3 via thethrough-hole 32.

Also, in the embodiment bf FIG. 6, the forming mold A and a mold clampmechanism 40 are supported on a carrier base 6, which is moved on aguide rails 61 through wheels 62 and 63 mounted on a lower surfacethereof. The carrier base 6 is mounted on a rear end thereof or aleft-hand end thereon in FIG. 6 with a frame plate member 64, which hasa piston 66 connected thereto so as to forwardly extend therefrom. Thepiston 66 is arranged so as to be reciprocated in a hydraulic cylinder65. The hydraulic cylinder 65 is fixed on a suitable support (not shown)and functions to apply a hydraulic pressure to the piston 66 to move thecarrier base 6. Thus, in the illustrated embodiment, the carrier base 6,guide rails 61, wheels 63, frame plate member 64, hydraulic cylinder 65and piston 66 cooperate with each other to provide an access mechanism60. Alternatively, the illustrated embodiment may be so constructed thatthe carrier base 6 may be freely moved by a pressure due to extrusion ofbiodegradable resin without arrangement of the hydraulic cylinder 65 andpiston 66. In this instance, an actuation control mechanism 7 includingan electromagnet and having a field current adjustment section 71connected thereto is arranged on the wheel 62 to control a speed ofretraction of the carrier base 6. The remaining part of the illustratedembodiment may be constructed in substantially the same manner as theembodiment described above with reference to FIG. 1.

The manner of operation of the apparatus of FIG. 6 constructed asdescribed above will be described hereinafter. The apparatus is adaptedto extrude fluidized biodegradable resin into the forming mold whileplacing the nozzle arranged with respect to the narrowed opening in thedepths of the forming mold at the time when operation of the nozzle isstarted and retracting the nozzle relative to the forming mold duringextrusion of the biodegradable resin.

More particularly, the forming mold A is kept clamped and the carrierbase 6 is positioned at a forward position so that a distal end of thenozzle 12 arranged at the narrowed opening 1 a is positioned in thedepths of the forming mold A. Such arrangement of the nozzle 1 may beattained through a stopper provided on, for example, the guide rail 61.Then, particles 10 of biodegradable resin and moisture are fed to ahopper 1 and forwardly forcibly transferred in the cylinder 2 by meansof a screw 2, during which the biodegradable resin particles 10 areincreased in temperature to a level near a softening point of the resinor a melting point thereof by shearing force due to rotation of thescrew 2 and heat applied thereto from the heater 13. This results in thebiodegradable resin being collected in an inner space of the cylinder 1defined on a side of a distal end of the screw 2 while being fluidized.

At this time, the inner space of the cylinder 1 is kept heated andpressurized, so that moisture contained in the biodegradable resinparticles 10 is kept trapped in the biodegradable resin withoutevaporating therefrom. Then, rotation of the screw 2 is stopped and apiston 23 in an injection cylinder 22 is actuated to advance the screw 2as shown in FIG. 7(a), so that the fluidized biodegradable resin may beinjected from the cylinder 1 through the nozzle 12 into a forming spaceR in the forming mold A at a stretch.

This causes the biodegradable resin to be rapidly exposed to anatmospheric pressure, so that moisture trapped in the resin is caused toinstantaneously evaporate from the resin to foam the resin and theforming mold A is retracted rearwardly or in a left-hand direction inFIG. 7 by a hydraulic pressure of the hydraulic cylinder 65. Thisresults in the biodegradable resin successively foaming while beingextruded in order from a side of the depths of the forming mold A. Aspeed at which the forming mold A is retracted is adjusted by hydrauliccontrol of the hydraulic cylinder 65. An excessive increase in speed ofthe forming mold A causes an excessive amount of biodegradable resin tobe extruded in an entrance section of the forming mold A, leading topositionally non-uniform foaming of the resin; whereas an excessivedecrease in speed of the mold A causes cells of biodegradable resinfoamed in the depths of the mold A to be collapsed by biodegradableresin extruded subsequently thereto. Thus, it is desirable that a speedof retraction of the forming mold A is determined so as to permit thebiodegradable resin to be successively extruded in a suitable amount inturn from a side of the depths of the mold A. Expansion force of watervapor occurs in the biodegradable resin. However, an outermost portionof the biodegradable resin is kept contacted with the forming mold A, tothereby regulated by a configuration of a cavity 31 and the water vaporis outwardly discharged through pores of the forming mold A, so that abiodegradable resin foam B integrally formed may be obtained. Then, thescrew 2 is retracted while being rotated as shown in FIG. 7(c), duringwhich collection of the next biodegradable resin fluidized in the innerspace of the cylinder 1 on the side of the distal end of the screw 2starts for the next injection. Concurrently, the biodegradable resinfoam product formed in the cavity 31 of the forming mold A is allowed tobe cooled and solidified, so that releasing of the forming mold A fromclamping by the clamp mechanism 40 permits the resin foam B to beremoved from the cavity 31, followed by clamping of the mold A for thenext operation.

As noted from the above, the illustrated embodiment is so constructedthat the nozzle 12 is initially positioned in the depths of the formingmold A and then successively retracted while extruding the biodegradableresin into the forming mold A, to thereby permit extrusion of thebiodegradable resin to be carried out while keeping a portion of aninner space of the mold to be subsequently charged with thebiodegradable resin and an extrusion port of the nozzle 12 in proximityto each other. Thus, the illustrated embodiment constantly keeps thebiodegradable resin successively extruded into a portion of the formingmold A at which foaming of the resin is desired. This permits thefoaming to be completed while ensuring that the biodegradable resinextends well through the forming mold A, to thereby substantiallyeliminate the above-described disadvantage that foamed cells of thebiodegradable resin collected while being separated from an innersurface of the forming mold A are forced by the following biodegradableresin, resulting in being collapsed. Thus, the biodegradable resin foamB produced by the apparatus of the illustrated embodiment can beconstructed into a desired configuration and uniformity sufficient toexhibit satisfactory cushioning properties.

In the illustrated embodiment, relative movement between the formingmold A and the nozzle 12 is accomplished by movement of the forming moldA retractably constructed. Alternatively, it may be attained byconstructing the injection machine S in a retractable manner. Also, bothmay be retractably constructed. A speed of relative movement between themold A and the nozzle 12 may be controlled through, for example, thehydraulic cylinder 65. Such construction permits foaming density(filling degree) of the biodegradable resin foam B to be controlled, tothereby vary properties of the foam B. For example, this permits thefoam B to be formed so as to have a hardened surface and a softenedinner layer.

The nozzle 12 may be formed at an outlet port thereof into a diameterdecreased to a degree sufficient to permit the biodegradable resin to beinjected while being atomized. This permits the biodegradable resin foamof satisfactory properties to be produced even when the forming mold Ais formed into a complicated configuration. Also, the illustratedembodiment may be modified in such a manner as shown in FIG. 8. In amodification of FIG. 8, a forming mold A and a mold clamp mechanism 40are received in a chamber 5 constructed in an airtight manner. Also, apressure reducing pipe L₁ provided with a pressure reducing pump P₁ anda pressure reducing valve V₁ and an atmospheric pressure releasing pipeL₀ provided with an atmospheric pressure releasing valve V₀ areconnected to the chamber 5 to reduce a pressure in the chamber 5 throughactuation of the pressure reducing pump P₁. Such construction permitswater vapor generated from biodegradable resin to be forcibly outwardlydischarged from a circumference of the forming mold A, to therebysubstantially restrain shrinkage of a biodegradable resin foam due tore-adhesion of water vapor contributing to foaming of biodegradableresin to the foam. Alternatively, such an advantage can be exhibitedalso by ventilation of the chamber 5 rather than pressure reduction inthe chamber. In this instance, the chamber 5 and mold clamp mechanism 40may be constructed so as to surround the forming mold A and locatedoutside the chamber 5, respectively.

In the method for producing the biodegradable resin foam according tothe present invention, the step of extruding the fluidized biodegradableresin into the forming mold may be carried out in a manner to keep anatmosphere in the forming mold pressurized during the extrusion andrapidly reduce a pressure of the atmosphere in the forming mold aftercompletion of the extrusion. This may be carried out by means of anapparatus constructed in such a manner as shown in FIG. 9.

The apparatus shown in FIG. 9 includes a chamber 5 having a pressuringpipe L₃ and a pressure reducing and releasing pipe L₄ connected thereto,other than the pressure reducing pipe L₁, pressure reducing valve V₁ andpressure reducing pump P₁ arranged in the apparatus shown in FIG. 1. Thepressuring pipe L₃ is connected through a pressuring valve V₃ to acompressor C to pressurize an atmosphere in the chamber 5. The pressurereducing and releasing pipe L₄ corresponds to the atmospheric pressurereleasing pipe L₀ arranged in the apparatus shown in FIG. 1 and isarranged so as to communicate through a pressure reducing and releasingvalve V₄ to an ambient atmosphere. The remaining part of the apparatusmay be constructed in substantially the same manner as the apparatusshown in FIG. 1.

Now, the extrusion step executed by means of the apparatus of FIG. 9constructed as described above will be described hereinafter. First, theforming mold A is kept clamped and the chamber 5 acting as a pressureadjusting chamber is kept pressurized by the compressor C. Then, asshown in FIG. 9, a hopper 11 is fed with particles 10 of moisture andbiodegradable resin which constitute a biodegradable resin startingmaterial. The starting material is then forcibly forwardly transferredin the cylinder 1 by means of a screw 2, during which the biodegradableresin particles 10 are increased in temperature to a level near asoftening point of the resin or a melting point thereof by shearingforce due to rotation of the screw 2 and heat applied thereto from aheater 13. This results in the biodegradable resin being collected in aninner space of the cylinder 1 defined on a distal end side of the screw2 while being fluidized.

At this time, the inner space is kept heated and pressurized, so thatmoisture contained in the biodegradable resin particles 10 is kepttrapped in the biodegradable resin without evaporating therefrom. Then,rotation of the screw 2 is stopped and a piston 23 in an injectioncylinder 22 is actuated to advance the screw 2 as shown in FIG. 10(a),so that the fluidized biodegradable resin may be injected from thecylinder 1 through a narrowed opening 1 a into a forming space R in theforming mold A at a stretch.

An inner space of the chamber 5 is kept pressurized, so that a cavity 31and a core 41 of an air-permeable forming mold A communicating throughpores of the forming mold A with the inner space of the chamber 5 islikewise pressurized. In this instance, when a pressure in the formingspace R defined by the cavity 31 and core 41 is set at a level of, forexample, 10 kgf/cm² higher than a water vapor pressure at a temperatureof the biodegradable resin injected through the narrowed opening or port1 a or, for example, at 170° C., the biodegradable resin may be extrudedinto the forming space R while keeping moisture trapped therein.

After the biodegradable-resin is charged in the forming space R of theforming mold A, the pressure reducing and releasing valve V₄ is rapidlyand fully rendered open to permit a pressure in the chamber 5 to bereduced to an atmospheric pressure, so that the biodegradable resin in aheated and pressurized state is rapidly exposed to an atmosphericpressure, resulting in moisture trapped in the resin beinginstantaneously vaporized to foam the biodegradable resin. Also,vaporization of the moisture causes expansion force of water vapor tooccur in the biodegradable resin. However, an outermost portion of thebiodegradable resin is kept contacted with an outer surface of theforming mold A, to thereby be regulated by a configuration of the cavity31 and core 41 and the water vapor is outwardly discharged through thepores of the forming mold A, so that such a biodegradable resin foam Bintegrally formed as shown in FIG. 3 may be obtained.

Then, the screw 2 is retracted while being rotated as shown in FIG.10(c), during which collection of the following biodegradable resinfluidized in the inner space of the cylinder 1 on the side of the distalend of the screw 2 starts for the next injection. Concurrently, thebiodegradable resin foam B formed in the cavity 31 of the forming mold Ais allowed to be cooled and solidified, so that releasing of the formingmold A from the clamping permits the resin foam B to be removed from thecavity 31, followed by clamping of the forming mold A for the nextoperation.

In the method described above, the forming space R defined by the cavity31 and core 41 is kept pressurized until the fluidized biodegradableresin is injected from the cylinder 1 through the narrowed opening 1 ainto the forming space R, to thereby prevent foaming of thebiodegradable resin. Then, a pressure in the forming space R is rapidlydecreased to lead to foaming of the resin, so that the biodegradableresin foam B obtained may conform to a configuration of the forming moldA and exhibit uniformity, resulting in being effectively applied to asatisfactory cushioning material.

Thus, in the method practiced by means of the apparatus of FIG. 9, atiming of foaming of the biodegradable resin extruded through thenarrowed opening 1 a is adjusted by reducing a pressure in the chamber5. The timing of pressure reduction or foaming is not limited to settingafter the biodegradable resin is fully filled in the-forming space R.The pressure reduction may be carried out in the course of extrusion ofthe resin ,through the narrowed opening 1 a into the forming space R.Thus, the timing may be suitably set depending on, for example, a speedat which the biodegradable resin is extruded through the narrowedopening 1 a, a temperature at which the biodegradable resin is heated,and the like.

A pressure in the chamber 5 may be reduced to a level lower than, equalto or higher than an atmospheric pressure. Reduction of the pressure toa level lower than an atmospheric pressure permits a pressure differenceobtained to be substantially increased, resulting in foaming of thebiodegradable resin being carried out to an increased degree. Also, thisleads to discharge of water vapor to an exterior of the chamber 5, tothereby prevent shrinkage of the biodegradable resin foam due tore-adhesion of moisture once contributing to the foaming to the resinfoam.

The apparatus of FIG. 9 may be modified in such a manner as shown inFIG. 11. More particularly, an apparatus of FIG. 11 is so constructedthat a chamber 5 is divided into a movable-side part 51 and a fixed-sidepart 52 and the movable-side part 51 is arranged so as to be movableintegrally with a movable mold part 4. Such construction permits aforming mold A and the chamber 5 to be concurrently operated, to therebyfacilitate removal of a As biodegradable resin foam from the formingmold A and chamber 5.

In the method of the present invention, extrusion of the fluidizedbiodegradable resin into the forming mold is carried out by injectingthe biodegradable resin into the forming mold while keeping the resinatomized. Such extrusion may be executed by means of an apparatus asshown in FIG. 12. Therefore, the apparatus of FIG. 12 will be describedprior to description of the extrusion step.

In the apparatus of FIG. 12, a cavity 31 is formed into a rectangularshape and more particularly a rectangular parallelepiped shape and acore 41 is formed into a small rectangular parallelepiped shapecommunicating with the cavity 31. Also, a narrowed opening 1 a is formedinto a diameter smaller than that of a nozzle of a conventionalinjection molding machine, to thereby ensure that fluidizedbiodegradable resin in a heated and pressurized state may be injectedthrough the narrowed opening 1 a into a forming space R defined by thecavity 31 and core 41 while being kept atomized. More particularly, thenozzle of the conventional injection molding machine is formed into adiameter of, for example, 2 to 5 mm, whereas in the illustratedembodiment, the narrowed opening 1 a is formed into a diameter as smallas about 1 mm.

The extrusion by means of the apparatus shown in FIG. 12 is initiated byfeeding a hopper 11 with particles 10 of moisture and biodegradableresin while keeping a forming mold A clamped. Then, the particles 10, asshown in FIG. 13(a), are forwardly forcibly transferred in a cylinder 1by means of a screw 2, during which the particles 10 are heated to atemperature near a softening point of the particles or a melting pointthereof by shearing force due to rotation of the screw 2 and heatapplied to the particles from a heater 13 and then collected in an innerspace of the cylinder 1 defined on a side of a distal end of the screw 2while being fluidized. At this time, the inner space of the cylinder 1is kept heated and pressurized, so that moisture contained in thefluidized biodegradable resin is trapped-therein without evaporatingtherefrom.

Then, as shown in FIG. 13(b), rotation of the screw 2 is stopped and apiston 23 in an injection cylinder 22 is actuated to advance the screw2, resulting in the fluidized biodegradable resin being injected at astretch through the narrowed opening 1 a into the forming space Rdefined by the cavity 31 and core 41 while being kept atomized.

Injection of the resin while keeping it atomized may be carried out byforming the narrowed opening 1 a into a small diameter as compared withthat of the conventional injection molding machine and suitablyadjusting a speed of injection of the fluidized resin and a differencebetween a pressure before the extrusion and that after the extrusion. Adiameter of the narrowed opening 1 a required for atomization of theresin is not limited to the above-described value of about 1 mm becauseit is also varied depending on a speed of extrusion of the fluidizedresin as well.

An exterior of the forming mold A is permitted to communicate with anambient atmosphere, resulting in the forming space R being kept at anatmospheric pressure because it likewise communicates through pores ofthe mold A with an ambient atmosphere. Thus, the biodegradable resininjected at a stretch into the forming space R while being atomized israpidly exposed to an atmospheric pressure, so that moisture trapped inthe resin is instantaneously vaporized to foam the biodegradable resin.Expansion force of the vaporized moisture or water vapor is exerted inthe biodegradable resin, however, an outermost portion of the foamedresin is kept contacted with an inner surface of the forming mold A,resulting in being regulated by a configuration of the space R. Then,the water vapor formed is discharged through the pores of the formingmold A to an exterior of the mold A. Foaming of the biodegradable resinis carried out for every particle, resulting in foamed cells 100 beingformed. The foamed particles are entangled with each other and meltedwith each other, leading to a biodegradable resin foam B integrallyformed.

Then, as shown in FIG. 13(c), the screw 2 is retracted while beingrotated, during which the following biodegradable resin fluidized iscollected in the inner space of the cylinder 1 on the side of the distalend of the screw 2 for the next operation and the biodegradable resinfoam B in the forming space R of the forming mold A is allowed to becooled and solidified. Then, the forming mold A is released fromclamping by the mold clamp mechanism, so that the biodegradable resinfoam B may be removed from the mold A, followed by re-clamping of themold A for the next operation.

In the method described above, the biodegradable resin fluidized isinjected to the forming space R of an atmospheric pressure while beingatomized, resulting in being spread throughout the forming-space Rirrespective of a configuration thereof. Also, this permits theparticles constituting the atomized biodegradable resin to foam whilebeing collected together. Therefore, even when the forming space R ofthe forming mold A is formed into a complicated shape, the methodminimizes or substantially eliminates a disadvantage that the foamedcells of the biodegradable resin are collected at positions away from aninner surface of the forming mold, resulting in the foamed cells beingcollapsed due to forcing by subsequently extruded biodegradable resin.Thus, the biodegradable resin foam B obtained fully conforms to aconfiguration of the forming mold and exhibits uniformity, resulting inbeing effectively applied to a satisfactory cushioning material.

In the apparatus of the illustrated embodiment, an exterior of theforming mold A may be exposed to an atmosphere ventilated. This permitsthe water vapor to be forcibly outwardly discharged from the formingmold A, to thereby exhibit an advantage of effectively preventingmoisture which has once contributed to foaming of the biodegradableresin from re-adhering to the resin foam, to thereby prevent shrinkageof the foam.

The forming mold A may be arranged in the chamber 5 to reduce a pressurein an atmosphere outside the forming mold A to a level below anatmospheric pressure. This permits a difference between a pressureoutside the forming mold A and that inside the mold to be increased, sothat the resin may be foamed to an increased degree and forced dischargeof water vapor from the mold is increased to minimize condensation ofthe water vapor on the resin foam.

Also, in the illustrated embodiment, at least one nozzle 12 may bearranged with respect to the narrowed opening 1 a as shown in FIG. 14.In FIG. 14, a plurality of such nozzles 12 are arranged on the cylinder1. Alternatively, the cylinder 1 may be provided at a distal end thereofwith a shower 15 formed with a plurality of fine injection ports 14.Also, when the embodiment is so constructed that-the biodegradable resinis injected into the forming mold A through a runner and a gate (notshown), the runner and gate each may be formed into a small diameter toensure that the injection is carried out while keeping it atomized.

Further, the apparatus of the illustrated embodiment may be constructedin such a manner as shown in FIG. 16. More particularly, the chamber 5is divided into a plurality of pressure reducing chambers 53, 54 and 55which are constructed so as to be airtight with respect to each otherand arranged so as to surround the forming mold A. The chambers 53, 54and 55 have pressure reducing pipes L₁ connected thereto, respectively.Thus, a degree of pressure reduction in each of the chambers may bevaried through the pressure reducing pipe L₁, to thereby adjust fillingof the biodegradable resin in of the forming space R of the forming moldA while being kept atomized, so that it may be charged in the formingspace R in turn form the depths thereof with high efficiency. In thisinstance, the chamber 5 may be constructed so as to be operated insynchronism with the forming mold A.

In the method of the present invention, the biodegradable resin startingmaterial may comprise moisture, biodegradable resin and a waterrepellent material. An apparatus suitable for practicing the methodusing the biodegradable resin starting material of such composition isshown in FIG. 17, which apparatus may be constructed in substantiallythe same manner as that shown in FIG. 1, except that the chamber 5 iseliminated. Particles 10 of biodegradable resin which contains asubstantial amount of moisture and a water repellent material arecharged in a hopper 11 and then forcibly forwardly transferred in acylinder 1 by means of a screw 2, during which the biodegradable resinparticles 10 are increased in temperature to a level near a softeningpoint of the resin or a melting point thereof by shearing force due torotation of the screw 2 and heat applied thereto from a heater 13 or alevel, for example, of about 170° C. This results in the biodegradableresin being collected in an inner space of the cylinder 1 defined on adistal end side of the screw 2 while being fluidized.

At this time, the inner space of the cylinder 1 is kept heated andpressurized, so that moisture contained in the biodegradable resinparticles 10 is kept trapped in the biodegradable resin withoutevaporating therefrom. Then, rotation of the screw 2 is stopped and apiston 23 in an injection cylinder 22 is actuated to advance the screw2, so that the fluidized biodegradable resin may be injected through anarrowed opening 1 a from the cylinder into a forming space R of theforming mold A at a stretch.

This causes the biodegradable resin in a heated and pressurized state tobe rapidly exposed to an atmospheric pressure, resulting in moisturetrapped in the resin being instantaneously vaporized to foam thebiodegradable resin. The above-described water repellent material has aboiling point higher than that of water, so that most of the waterrepellent material remains as a film on a surface of each of cells ofthe foamed biodegradable resin. Vaporization of the moisture causesexpansion force of water vapor to occur in the biodegradable resin.However, an outermost portion of the biodegradable resin is keptcontacted with an inner surface of the forming mold A, to thereby beregulated by a configuration of a forming space defined by a cavity 31and a core 41, so that such a biodegradable resin foam B integrallyformed as shown in FIG. 19 may be obtained.

Then, the screw 2 is retracted while being rotated as shown in FIG.18(b), so that the following biodegradable resin fluidized is collectedin the inner space of the cylinder 1 on the side of the distal end ofthe screw 2 for the next injection. Concurrently, the biodegradableresin foam B formed in the cavity 31 of the forming mold A is allowed tobe cooled and solidified, so that releasing of the forming mold A fromclamping by a mold clamp mechanism permits the resin foam B to beremoved from the cavity 31, followed by clamping of the mold A for thenext operation.

In the method described above, the water repellent material forms a filmfor covering each of foamed cells of the biodegradable resin foam, tothereby effectively prevent the foamed cells from being collapsed orbroken due to swelling and/or softening of the biodegradable resincaused by contact of the resin foam with water. More particularly,formation of the film exhibits a first advantage of preventing moisturewhich has once contributed to foaming of the biodegradable resin due tovaporization and expansion thereof from re-adhering to the foam productand a second advantage of minimizing softening and swelling of the resinfoam in use. Also, when a natural fatty acid polymer may be used as thewater repellent material, the whole biodegradable resin foam exhibitssatisfactory biodegradable properties because the polymer is likewisebiodegradable.

The apparatus of the illustrated embodiment may be modified in such amanner as shown in FIG. 20. More particularly, in a modification of FIG.20, a forming mold A is arranged in an airtight chamber 5 which can bedivided into a movable-side part 51 and a fixed-side part 52, so that apressure reducing valve V₁ is rendered open at a predetermined timingsuch as, for example, in a one second before or after extrusion of thebiodegradable resin through a narrowed port 1 a into a forming mold A,to thereby reduce a pressure in the chamber 5 through a A pressurereducing pipe L₁ by means of a pressure reducing pump P₁. Alternatively,the illustrated embodiment may be constructed in substantially the samemanner as the apparatus described above with reference to FIG. 5,wherein the forming mold A is arranged in the ventilation duct D whichis forcibly ventilated by means of the suction fan f. Such constructionseach permit moisture to be forcibly removed from the forming mold A, tothereby more positively prevent shrinkage of the biodegradable resin. InFIG. 20, reference character L₀ designates an atmospheric pressurereleasing pipe and V₀ is an atmospheric pressure releasing valvearranged in the middle of the pipe L₀.

In the illustrated embodiment, the biodegradable resin particles 10,moisture and water repellent material are charged separately in thehopper 11. Alternatively, the cylinder 1 may be provided with an inletport, through which the moisture or water repellent material may be feddirectly to the cylinder 1. Also, the illustrated embodiment may providea single biodegradable resin foam through the forming mold A by eachbatch production. Alternatively, the resin foam may be extruded througha cap, to thereby be obtained in the form of a continuous rod of asuitable sectional configuration corresponding to a configuration of thecap. In this instance, a plurality of the rod-like resin foams whichhave been extruded or is being foamed are combined with each other toprovide a continuous rod-like product of an increased thickness.

Further, an air-permeable cylinder in place of the forming mold A may bearranged in front of the narrowed opening la, so that a plurality offoam products extruded through the cylinder are joined in parallel toeach other by means of an adhesive. Alternatively, the resin foams arejoined together immediately after the formation, resulting in beingadhered together by means of moisture on the surface. Thus, a singlecontinuous resin foam may be provided.

The present invention is not limited to foaming by extrusion through aninjection molding machine or the like. For example, the presentinvention may be conveniently applied to foaming practiced according toa procedure wherein the air-permeable foaming mold A is arranged in aclosed heating vessel, a predetermined amount of biodegradable resincontaining a water repellent material is charged in the forming mold A,heated water vapor is introduced into the heating vessel and then apressure in the heating vessel is reduced. Also, in the presentinvention, the step of foaming the biodegradable resin and the step ofsubjecting the foamed resin to formation may be carried out separately.

Now, embodiments of an apparatus of the present invention which isfeatured in a pressure adjusting mechanism arranged in a forming mold Aand embodiments of a method of the present invention practiced by meansof the apparatus of such a featured structure will be describedhereinafter.

Referring first to FIG. 21, an embodiment of an apparatus of the presentinvention is illustrated. In an apparatus of the illustrated embodiment,it is desirable that a narrowed opening 1 a or a nozzle 12 provided atthe narrowed opening 1 a is formed into a diameter of about 6 mm. Also,when the nozzle 12 is arranged at the narrowed opening 1 a, the nozzle12 is preferably equipped with a shut-off valve.

Now, the apparatus of FIG. 21 will be substantially described inconnection with differences between the apparatus of FIG. 21 and thatshown in FIG. 1. The apparatus of FIG. 21 includes a chamber 5 arrangedat a distal end of an injection machine S so as to act as a pressureadjusting chamber. In the illustrated embodiment, the chamber 5 isconstituted by a mold of a so-called injection molding machine andincludes a fixed mold part 3 formed with a cavity 31 communicating withthe narrowed opening 1 a and a movable mold part 4 formed with a core41. The fixed mold part 3 and movable mold part 4 are mounted on afixed-side mold plate 40A of a mold clamp mechanism 40 and amovable-side mold plate 40B thereof, respectively. The cavity 31 isformed into, for example, a rectangular shape and cooperates with thecore 41 likewise formed into a rectangular shape to provide a formingspace R, in which an air-permeable forming mold A is arranged.

In the illustrated embodiment, the forming space R for the forming moldA is formed into a rectangular configuration having a L-shape in sectionas a corner angle and the forming space R is fixedly positioned by meansof a positioning rod 30 arranged in the chamber 5. However, the formingspace R for the forming mold A is limited to any specific configuration.Therefore, a plurality of such forming molds A different inconfiguration which are previously prepared may be suitably replacedwith each other as desired. In the illustrated embodiment, the chamberand mold clamp mechanism 40 are open to an ambient atmosphere.

The chamber 5 has a pressure reducing pipe L₁ connected thereto, whichis provided in the middle thereof with a pressure reducing valve V₁ andthen connected through the pressure reducing valve V₁ to a pressurereducing tank T₁. The pressure reducing tank T₁ is also connectedthereto a pressure reducing pump P₁ The pressure reducing tank T₁ isreduced in pressure to a predetermined level near, for example, a vacuumand is adapted to communicate with the chamber 5 when the pressurereducing valve V₁ is open. The pressure reducing tank T₁ is required tohave a volume sufficient to permit a pressure in the chamber 5 to berapidly reduced when it communicates with the chamber 5. The remainingpart of the apparatus of the illustrated embodiment may be constructedin substantially the same manner as the apparatus shown in FIG. 1.

Now, formation of a biodegradable resin foam by means of the apparatusof the illustrated embodiment will be described hereinafter withreference to FIG. 21.

First, the chamber 5 is clamped by the mold clamp mechanism 40 andclosed while keeping an inner space thereof at, for example, anatmospheric pressure. Biodegradable resin fluidized as previouslydescribed is injected at a stretch from a cylinder 1 through thenarrowed opening 1 a into the forming mold A. After the injection, thepressure reducing valve V₁ is rendered open to communicate the pressurereducing tank T₁ with is the chamber 5, to thereby rapidly reduce apressure in the chamber 5 to a gauge pressure of, for example, about 750mmHg. This causes moisture trapped in the biodegradable resin to beinstantaneously vaporized to foam the resin. The resultant water vaporis caused to be discharged at a stretch through pores of the formingmold A to the pressure reducing tank T₁. Concurrently, expansion forcedue to vaporization of the water vapor is exerted in the biodegradableresin, however, an outermost portion of the resin is kept contacted withthe forming space R defined by the cavity 31 and core 41, resulting inbeing regulated by a configuration of the space R. Thus, a biodegradableresin foam of a predetermined configuration is provided.

Then, the pressure reducing valve V₁ is closed to interruptcommunication between the pressure reducing tank T₁ and the chamber 5and then a screw 2 is retracted while being rotated, during which thefollowing or subsequent biodegradable resin is collected in an internalspace of the cylinder 1 defined on a side of a distal end of the screw 2while being fluidized, resulting in being ready for the next operation.Concurrently, the pressure reducing pump P₁ is actuated to reduce apressure in the pressure reducing tank T₁ to the initial level again,during which the biodegradable resin foam in the forming mold A isallowed to be cooled and solidified. Then, the movable mold part 4 ismoved away from the fixed mold part 3 to open the forming mold A, sothat the biodegradable resin foam may be removed from the mold A,followed by re-clamping of the mold A for the next operation.

The apparatus of the illustrated embodiment may be modified in such amanner that the chamber acting as the pressure adjusting chamber mayhave an evacuation valve connected thereto, as shown in FIG. 22. Moreparticularly, an apparatus of FIG. 22 includes an evacuation pipe L₂connected between a pressure reducing valve V₁ of a pressure reducingpipe L₁ connected to a chamber 5 or pressure adjusting chamber 5 and thechamber 5. The evacuation pipe L₂ is provided in the middle thereof withan evacuation valve V₂ and the evacuation pipe L₂ is exposed at anoutlet thereof to an atmospheric pressure. The remaining part of theapparatus of FIG. 22 may be constructed in substantially the same manneras the apparatus of FIG. 21.

When the evacuation valve V₂, as shown in FIG. 23, is rendered open inthe course of injection of biodegradable resin into a forming mold A bymeans of an injection machine S to expose an interior of the chamber 5to an atmospheric pressure. After the injection, the evacuation valve V₂is closed and the pressure reducing valve V₁ is open to permit thepressure reducing tank T₁ to communicate with the chamber 5, resultingin a pressure in the chamber being rapidly reduced. A timing at whichthe evacuation valve V₂ is rendered open may be set between starting ofthe injection and termination thereof, therefore, the timing is notlimited to any specific setting. It is determined depending on variousfactors such as a configuration of the forming mold A, a size of thechamber 5, a degree to which the cylinder 1 is pressurizedduringsinjection of the biodegradable resin, and the like.

In the modification of FIG. 22, the evacuation pipe L₂ is open at theoutlet thereof to an atmospheric pressure, however, the modification isnot limited to such construction. For example, the evacuation may beforcibly carried out under a reduced pressure formed by means of thepressure reducing pump P₁ or the like. In the apparatus shown in FIG.21, resistance to the injection may be reduced by delaying a timing atwhich access between the fixed mold part 3 and the movable mold part 4is carried out in a state that air is somewhat accessible to the mold bymeans of an actuation mechanism 44 of the mold clamp mechanism 40,tightly clamping the forming mold concurrently with termination ofinjection of the biodegradable resin into the forming mold, and thenopening the pressure reducing valve V₁. Such construction requirescontrol for carrying out association between actuation of the actuationmechanism 44 of the mold clamp mechanism 40 and operation of thepressure reducing valve V₁, as well as a controller therefor. This maybe applied to additional embodiments of the present invention describedhereinafter which is operated under pressure and is not provided withthe evacuation valve V₂.

FIGS. 24 and 25 each show another embodiment of an apparatus of thepresent invention, which is generally constructed in such a manner thata chamber has a compressor connected thereto. More particularly, in theembodiment of FIG. 24, a chamber 5 acting as a pressure adjustingchamber has a pressurizing pipe L₃ connected thereto, which is providedin the middle thereof with a pressuring valve V₃ and connected throughthe pressuring valve V₃ to a compressor C. The pressurizing valve V₃ isopen at the time when or before injection of biodegradable resin into aforming mold A by means of an injection machine S is started, to therebypressurize the chamber 5 through the compressor C. After the injection,the pressurizing valve V₃ is closed to interrupt pressurization of thechamber 5 through actuation of the compressor C and a pressure reducingvalve V1 is open to permit a pressure reducing tank T₁ to communicatewith the chamber 5 to rapidly reduce a pressure in the chamber. Theremaining part of the embodiment of FIG. 24 may be constructed insubstantially the same manner as the apparatus shown in FIG. 21.

Pressurization of the chamber 5 is carried out to obtain a pressurehigher than a saturated water vapor pressure at a temperature at whichthe biodegradable resin is injected through a narrowed opening 1 a intoa forming mold A. For example, the pressure may be about 10 kg/cm² whenthe injection takes place at 170° C. When the chamber 5 has thecompressor C rather than a pressuring tank T₃ connected thereto throughthe pressurizing valve V₃ as described hereinafter, the pressurizingvalve V₃ may be kept open without being controlled or the pressurizingvalve V₃ may be eliminated.

In the embodiment of FIG. 25, a chamber 5 acting as a pressure adjustingchamber has a pressurizing pipe L₃ connected thereto, which is providedin the middle thereof with a pressuring valve V₃ and connected throughthe pressuring valve V₃ to a compressor C. The pressurizing valve V₃, asshown in FIG. 26, is rendered open at the time when injection ofbiodegradable resin into a forming mold A by means of an injectionmachine S is started, to thereby pressurize the chamber 5 through thecompressor C. In the course of the injection, the pressurizing valve V₃is closed to interrupt pressurization of the chamber 5 through thecompressor C and an evacuation valve V₂ is open, resulting in thechamber 5 being exposed to an atmospheric, pressure. After theinjection, the evacuation valve V₂ is closed and a pressure reducingvalve V₁ is open to permit a pressure reducing tank T₁ to communicatewith the chamber 5 to rapidly reduce a pressure in the chamber 5. Theremaining part of the embodiment of FIG. 25 may be constructed insubstantially the same manner as the apparatus shown in FIG. 22.

In addition, the apparatus of FIG. 21 may be constructed as in anembodiment shown in each of FIGS. 27 and 28, wherein a pressureadjusting chamber has a pressurizing tank connected thereto. Moreparticularly, in the embodiment of FIG. 27, a chamber 5 functioning as apressure adjusting chamber has a pressurizing pipe L₃ connected thereto,which is provided in the middle thereof with a pressurizing valve V₃ andconnected via the pressuring valve V₃ to a pressuring tank T₃, which isthen connected to a compressor C. The pressuring valve V₃ is kept openat the time when or before injection of biodegradable resin into aforming mold A by means of an injection machine S is started to permitthe pressurizing tank T₃ to communicate with the chamber 5, to therebyrapidly pressurize the chamber 5. After the injection, the pressurizingvalve V₃ is closed to interrupt communication between the tank T₃ andthe chamber 5 and a pressure reducing valve V₁ is rendered open to carryout communication between a pressure reducing tank T₁ and the chamber 5to rapidly reduce a pressure in the chamber 5. The remaining part of theapparatus of FIG. 27 may be constructed in substantially the same manneras the apparatus of FIG. 21.

In the embodiment of FIG. 28, a chamber 5 functioning as a pressureadjusting chamber has a pressurizing pipe L₃ connected thereto, which isprovided in the middle thereof with a pressurizing valve V₃ andconnected through the pressuring valve V₃ to a pressuring tank T₃ whichis then connected to a compressor C. The pressurizing tank T ispermitted to communicate with the chamber 5 at the time when or beforeinjection of biodegradable resin into a forming mold A by means of aninjection machine S is started, to thereby rapidly pressurize thechamber 5. In the course of the injection, the pressurizing valve V₃ isclosed to interrupt communication between the tank T₃ and the chamber 5and an evacuation valve V₂ is rendered open to expose the chamber 5 toan atmospheric pressure. After the injection, the evacuation valve V₂ isclosed and a pressure reducing valve V₁ is rendered open, to therebycarry out communication between a pressure reducing tank T₁ and thechamber 5, resulting in rapidly reducing a pressure in the chamber 5.The remaining part of the apparatus of FIG. 28 may be constructed insubstantially the same manner as the apparatus of FIG. 22.

Referring now to FIG. 29, a further embodiment of an apparatus of thepresent invention is illustrated. An apparatus of the illustratedembodiment includes a chamber 5 which serves as a pressure adjustingchamber and in which an air-permeable forming mold A is arranged. Thechamber 5 has a pressure reducing pipe L₁ and a pressurizing pipe L₃connected thereto. The pressure reducing pipe L₁ is connected thereto apressure reducing tank T₁ for rapid pressure reduction and thepressurizing pipe L₃ is connected thereto a compressor C. The pressurereducing pipe L₁ is provided in the middle thereof with a pressurereducing valve V₁. An evacuation pipe L₂ is connected to a portion ofthe pressure reducing pipe L₁ between the pressure reducing valve V₁ andthe chamber 5 and provided in the middle thereof with an evacuationvalve V₂. The evacuation pipe L₂ is open on an outlet side thereof to anambient atmosphere. Actuation of the compressor C for pressurization andoperation of each of the evacuation valve V₂ and pressure reducing valveV₁ are controlled by a valve controller 8. Reference character Sdesignates an injection machine for injecting, into a forming mold A,fluidized biodegradable resin in a heated and pressurized state in whichmoisture is trapped.

The pressurizing pipe L₃ is provided in the course thereof with apressuring valve V₃, which is operated in association with ON-OFFoperation of the compressor C. Alternatively, operation of thepressurizing valve V₃ may be carried out directly through the valvecontroller 8, so that the pressurizing valve V₃ may be eliminated. Also,the pressurizing valve V₃ may be left open without being controlled.

In general, a valve has a directional property in a passage thereof.Therefore, when the chamber 5 is concurrently provided with thepressuring valve V₃ and the pressure reducing valve V₁ or evacuationvalve V₂ as shown in FIG. 29, a valve free of any directional propertyis required to be used as each of the valves V₁ to V₃. Alternatively, itis required that arrangement of the valves is carried out not toadversely affect the pressurization and pressure reduction.

The valve controller 8 comprises a timer operated on the basis of, forexample, the time when injection of biodegradable resin into the formingmold A is started and is adapted to control operation of each of thevalves according to a timing chart shown in FIG. 26. For example, when astart button is turned on to start injection of the biodegradable resininto the forming mold A by means of the injection machine S, thepressurizing valve V₃ previously kept open is further kept open for apredetermined period of time set by the timer, during which thepressuring valve V₃ is rendered open and the compressor C kept turned oncauses a pressure in the chamber 5 to be increased. This results in thebiodegradable resin injected into the forming mold A being maintainedpressurized through pores of the air-permeable forming mold A, so thatmoisture is positively trapped in the biodegradable resin.

Then, the pressurizing valve V₃ is closed before completion of theinjection and concurrently the compressor C is turned off, resulting inactuation of the compressor for A pressurization being interrupted, andthe evacuation valve V₂ is kept open for a predetermined period of time.This causes the biodegradable resin being injected under pressure to beopen to an ambient atmosphere in the course of the injection, leading toa reduction in injection resistance, so that the biodegradable resin maybe spread throughout the forming model A. A timing at which thepressurizing valve V₃ is closed and concurrently the compressor C isturned off to open the evacuation valve V₂ is not necessarily definitelydetermined and is suitably adjusted depending on a configuration of theforming mold A, a volume of the chamber 5, a degree of thepressurization and evacuation, and the like.

After completion of the injection, the evacuation valve V₂ is closed andconcurrently the pressure reducing valve V₁ is kept open for apredetermined period of time. Thus, after the injection, the pressurereducing tank T₁ is permitted to communicate with the chamber 5 torapidly reduce a pressure in a forming space R of the forming mold A.This results in moisture trapped in the biodegradable resin beingvaporized at a stretch to form a biodegradable resin foam. Then, thepressure reducing valve V₁ is closed after a predetermined period oftime elapses.

The remaining part of the illustrated embodiment may be constructed insubstantially the same manner as the apparatus described above withreference to FIG. 1.

FIG. 30 shows still another embodiment of an apparatus of the presentinvention, which is constructed in substantially the same manner as theapparatus of FIG. 29 except that a pressuring tank T₃ is arrangedbetween a pressurizing valve V₃ and a compressor C.

The embodiment shown in each of FIGS. 29 and 30 may be so constructedthat the valve controller 8 controls so as to open the evacuation valveV₂ in the course of injection of the biodegradable resin into theforming mold A by means of the injection machine S, and close theevacuation valve V₂ and open the pressure reducing valve V₁ after theinjection without arrangement of the compressor C, pressurizing tank T₂and pressurizing valve V₂.

Also, the embodiment shown in each of FIGS. 29 and 30 may be soconstructed that the valve controller 8 controls so as to open thepressuring valve V₃ at the time when or before injection of thebiodegradable resin into the forming model A by means of the injectionmachine S is started, and close the pressuring valve V₃ and open thepressure reducing valve V₁ after the injection.

FIG. 31 shows yet another embodiment of an apparatus of the presentinvention, wherein a chamber 5 is arranged so as to surround both aforming mold A and a mold clamp mechanism 40. The chamber 5 has a sideplate 35 arranged so as to face an injection machine S, which side platemay be used as a mold plate.

FIG. 32 shows even another embodiment of an apparatus of the presentinvention, wherein a chamber 5 is arranged so as to surround a formingmold A and divided into a movable-side part 51 and a fixed-side part 52,resulting in the movable-side part 51 being movable integrally with amovable mold part 4 as indicated by phantom lines. Such constructionpermits a biodegradable resin foam to be readily removed due toconcurrent operation of the forming mold A and chamber 5 when the resinfoam is complicated in configuration.

FIG. 33 shows a still further embodiment of an apparatus of the presentinvention, wherein a chamber 5 is arranged so as to surround a formingmold A and fixedly mounted through a side plate 35A thereof on afixed-side mold plate 40A and through a side plate 35B thereof oppositeto the side plate 35A on a movable-side mold plate 40B, resulting inproviding a dual-type mold clamp mechanism. The remaining part of eachof the embodiments of FIGS. 31 to 33 may be constructed in substantiallythe same manner as the apparatus of FIG. 29.

In each of the embodiments described above, the chamber 5 may beprovided with a pressure gauge for suitably detecting whether a pressurein the chamber 5 is at an appropriate level. Also, the embodiments eachmay be so constructed that in order to prevent excessive pressurizationof the chamber 5 during the pressurization, the chamber 5 is providedwith a pressure sensor and a flow-rate varying valve is used as thepressuring valve V₃, to thereby to control a flow rate through the valveV₃ when the pressure sensor detects that a pressure in the chamber 5exceeds a predetermined level.

Also, in each of the embodiments, a plurality of the pressure reducingtanks T₁ and pressuring tank T₃ may be arranged so as to be successivelyalternately used for the purpose of permitting the apparatus of thepresent invention to produce the biodegradable resin foam B whileexhibiting improved productivity. More particularly, communication ofthe pressure reducing tank T₁ and/or pressuring tank T₃ with the chamber5 causes a pressure in the chamber 5 to be varied, so that production ofthe next biodegradable resin foam B requires to return the pressure toits original level. However, the pressure reducing pump P₁ andcompressor cause a period of time during which the pressure is returnedto the original state to be increased, leading to an increase in waitingperiod. The above-described alternate use of a plurality of the pressurereducing tanks T₁ and/or pressurizing tanks T₃ permits one of the tanksto be returned to the original state during operation of another tank,to thereby eliminate the waiting period, so that production of thebiodegradable resin foam may be carried out rapidly and in a repeatedmanner.

In production of the biodegradable resin foam B, the biodegradable resinmay consist of a first biodegradable resin ingredient of 100° C. or morein melting point and a second biodegradable resin ingredient having amelting point of 100° C. or less. The first biodegradable resiningredient may comprise polycaprolactone or a material containing it.The biodegradable resin may have polyhydric alcohols and derivativesthereof added thereto.

The method and apparatus of the present invention may be constructed soas to permit pressure reduction in the forming space R to beinstantaneously accomplished and the pressure reduction to be carriedout in a large scale or volume, resulting in improving quality of thebiodegradable resin foam B.

FIG. 34 shows an additional embodiment of an apparatus of the presentinvention which is constructed so as to accomplish such an object. Moreparticularly, an apparatus of the illustrated embodiment includes aforming mold A arranged forward of an injection machine S. The formingmold A includes a fixed mold part 3 formed with a cavity 31communicating with a narrowed opening 1 a and a movable mold part 4formed with a core 41. The fixed mold part 3 and movable mold part 4 aremounted on a fixed-side mold plate 40A of a mold operating mechanism forthe forming mold A and a movable-side mold plate 40B thereof,respectively. The cavity 31 is formed into, for example, a rectangularshape and cooperates with the core 41 to define a forming space R in theforming mold A. The fixed mold part 3 is provided with an inlet port 81,communication holes 82 for releasing airtightness of the forming space Rand an O-ring 83 for holding airtightness.

The forming space R of the forming mold A is tightly closed when thefixed mold part 3 and movable mold part 4 are clamped together by meansof the mold operating mechanism of the forming mold A. The moldoperating mechanism permits the movable mold part 4 to take a releasedposition O₁, an airtightly closed position O₂ an airtightness releasedposition O₃ and the released position O₁ in turn. The mold operatingmechanism includes tie bars 42 and 43 for guiding the fixed-side moldplate 40A and movable-side mold plate 40B so as to permit the fixed moldpart 3 and movable mold part 4 to access to each other while beingopposite to each other and an actuation mechanism 44 for accessiblyactuating the movable mold part 4.

Now, production of a biodegradable resin foam by means of the apparatusof FIG. 34 constructed as described above will be describe hereinafter.

First, the forming mold A is clamped by means of the mold operatingmechanism to close the forming space R while keeping a pressure in thespace R at a level of, for example, an atmospheric pressure. Then, ahopper 11 is fed with particles 10 formed of moisture and biodegradableresin. The particles 10 are then forwardly forcibly transferred in acylinder 1 by means of a screw 2, during which the particles 10 areheated to a temperature near a softening point of the particles 10 or amelting point thereof by shearing force due to rotation of the screw 2and heat applied thereto through the cylinder 1 from a heater 13,resulting in being collected in an inner space of the cylinder 1 definedon a side of a distal end of the screw in the cylinder 1 while beingfluidized. The inner space of the cylinder 1 is under heated andpressurized conditions, so that moisture contained in the particles 10is kept forcibly trapped in therein without evaporating therefrom.

Then, rotation of the screw 2 is stopped and a piston 23 in an injectioncylinder 22 is driven to advance the screw 2, so that the fluidizedbiodegradable resin may be injected at a stretch from the cylinder 1through the narrowed opening 1 a and inlet port 81 into the formingspace R. After the injection, the movable mold part 4 of the formingmold A is moved to the airtightness released position O₃ through themold operating mechanism, so that the forming space R is rapidly reducedin pressure to a level of an atmospheric pressure through thecommunication holes 82, so that moisture trapped in the fluidizedbiodegradable resin is instantaneously vaporized to foam the resin andthen outwardly discharged in the from of water vapor through thecommunication holes 82. At this time, expansion force due to formationof the water vapor is exerted in the foamed biodegradable resin,however, an outermost portion of the foamed resin is regulated by theforming space R defined by the cavity 31 and core 41, so that abiodegradable resin foam of a predetermined configuration may beproduced.

Then, the screw 2 is retracted while being rotated, during which thenext biodegradable resin fluidized is collected in the inner space ofthe cylinder defined on the side of the distal end of the screw 2 forthe next operation. During the period, the biodegradable resin foamformed in the forming space R is allowed to be cooled and solidified,thus, actuation of the mold operating mechanism permits the movable moldpart 4 to be moved to the released position O₁ for removal of the resinfoam B and then returned to the airtightly closed position O₂ for thenext operation.

FIG. 35 shows a yet further embodiment of an apparatus of the presentinvention, which is constructed in substantially the same manner as theapparatus shown in FIG. 34, except that an injection machine S iseliminated and a heating means 9 is provided for heating a forming moldA. The heating means 9 comprises, for example, a heater 91 arrangedoutside a fixed mold part 3. Reference numeral 92 designates a powersupply for heating.

Now, production of a biodegradable resin foam by means of the apparatusshown in each of FIGS. 34 and 35.

First, the movable mold part 4 of the forming mold A is moved to thereleased position O₁ by means of the mold operating mechanism. Then, thebiodegradable resin is placed in the forming space R defined by thecavity 31 and core 41 and then actuation of the mold operating mechanismcauses the movable mold part 4 to be moved to the airtightly closedposition O₂ to keep the forming space R airtight. Under such conditions,the forming mold A is heated by the heating means 9 to cause thebiodegradable resin to be fluidized. The forming space R is in a heatedand pressurized state, to thereby prevent moisture contained in thebiodegradable resin from-being vaporized, resulting in being forciblytrapped in the resin. Then, the movable mold part is moved to theairtightness released position O₃ through the mold operating mechanismto reduce a pressure in the forming space R to a level of an atmosphericpressure through the communication holes 82, so that moisture trapped inthe biodegradable resin may be instantaneously vaporized to foam theresin by expansion force due to vaporization of moisture and theresultant water vapor is outwardly discharged from the forming space Rthrough the communication holes 82, resulting in a biodegradable resinfoam of a desired configuration being produced in the forming space R.The resin foam is allowed to be cooled and solidified and then themovable mold part 4 is moved to the released position O₁ throughactuation of the mold operating mechanism, followed by removal of theresin foam therefrom. The above-described procedure is repeated for thenext operation.

Referring now to FIG. 36, even another embodiment of an apparatus of thepresent invention is illustrated. In FIG. 36, reference numeral 5designates a chamber, which is constituted by a mold M of a so-calledinjection molding machine and includes a fixed mold part m₁ formed witha cavity communicating with a narrowed opening 1 a and a movable moldpart m₂. The fixed mold part m₁ and movable mold part m₂ are mounted ona fixed-side mold plate 40A of a mold clamp mechanism and a movable-sidemold plate 40B thereof, respectively. The cavity is formed into arectangular shape and more particularly a rectangular parallelepipedshape, resulting in forming an inner chamber in the chamber 5, in whichan air-permeable press die N corresponding to the forming mold M isarranged.

The air-permeable press die N is formed with a plurality of pores whichpermit water vapor to pass through as in the forming mold A describedabove and may be made of a sintered metal material such as foamed metalsintered and formed, a sintered ceramic material such as ceramicsintered to which a void forming filler is added, or the like.Alternatively, it may be formed of a wire mesh, a punched metal plateformed with a number of holes or the like. The press die N is dividedinto an upper die part n₁ and a lower die part n₂, which are adapted tobe movable between a foaming position O₄ and a pressing position O₆through access mechanisms 60 a and 60 b, respectively.

The chamber 5 is tightly closed when the fixed mold part M₁ and movablemold part m₂ of the mold M are clamped together through the mold clampmechanism. The chamber and mold clamp mechanism may be arranged whilebeing exposed to an atmospheric pressure. The chamber 5 has a pressurereducing pipe L₁ connected thereto, which is provided in the middlethereof with a pressure reducing valve V₁ and connected to a pressurereducing pump P₁ through the pressure reducing valve V₁. A pressurereducing tank may be connected between the pressure reducing valve V₁and the pressure reducing pump P₁ as required.

Now, production of a biodegradable resin foam by means of the apparatusshown in FIG. 36 will be described hereinafter.

First, the pressure reducing valve V₁ is closed to render the chamber 5airtight and the upper and lower die parts n₁ and n₂ of the press die Nare positioned at the foaming position O₄. Then, biodegradable resinfluidized or melted is injected through the narrowed opening 1 a intothe press die N. Then, the pressure reducing valve V₁ is open to reducea pressure in the chamber 5, so that moisture trapped in the resin isinstantaneously evaporated or vaporized to foam the resin and theresultant water vapor is outwardly discharged through the pores of thepress die N and pressure reducing valve V₁. At this time, expansionforce due to vaporization of the water vapor is exerted in thebiodegradable resin, however, an outermost portion of the resin is keptcontacted with an inner surface of the press die N, so that a foamedportion of the resin is regulated by a configuration of the press die Nat the foaming position O₄. After the foaming, the upper and lower dieparts n₁ and n₂ of the press die N are rapidly moved to the pressingposition O₅ by means of the access mechanisms 60 a and 60 b,respectively, resulting in the forming space R being reduced in volume,so that the foamed resin may be compressed as compared with the initialfoamed state. Thus, any cavity and/or void occurring in the foamed resinin the initial foaming stage are extinguished due to the compression,thus, a biodegradable resin foam exhibiting satisfactory quality isprovided. Reduction of the forming space R after the foaming should becarried out under the condition that moisture still remains in theforming space R; because cells of the foamed resin are hard to adhere toeach other when cooling and solidification of the foamed resin aresubstantially advanced, resulting in the space R being substantiallyfree of water vapor.

The above-described construction of the apparatus of FIG. 36 may beincorporated in the apparatus of each of FIGS. 34 and 35. The apparatusof FIG. 34 may be constructed so as to move the movable mold part 4 ofthe forming mold A in an order of the released position O₁, theairtightly closed position O₂, the airtightness released position O₃,the pressing position and the released position O₁ rather than in anorder of the released position O₁. the airtightly closed position O₂,the airtightness released position O₂ and the released position O₁. Inthe illustrated embodiments, the airtightly closed position O₂ andpressing position O₅ are substantially the same.

Thus, after the forming, the movable mold part 4 of the forming mold Ais rapidly moved to the pressing position O₅ by means of the moldoperating mechanism to reduce a volume of the forming space R, so thatthe biodegradable resin foam is formed while being kept compressed ascompared with a volume thereof obtained in the initial foaming stage.This permits any cavity and/or void occurring in the initial foamingstage to be effectively extinguished, to thereby provide thebiodegradable resin foam with improved quality. Also, the forming spaceR is rendered open through the communication holes 82 to a pressurereduced atmosphere such as, for example, an ambient atmosphere after themovable mold part 4 is moved to the airtightness released position O₃,so that it may be instantaneously reduced in pressure in bulk, tothereby prevent softening and collapsing of the resin foam due tore-adhesion of moisture thereto, resulting in ensuring satisfactoryquality of the resin foam.

Also, the illustrated embodiment may be so constructed that the movablemold part 4 of the forming mold A takes the airtightness releasedposition O₃, pressing position O₅ and released position O₁ and is movedto the released position O₁, airtightness released position O₃, pressingposition O₅ and released position O₁ in order. Such construction permitsthe fluidized and water-trapped biodegradable resin in a heated andpressurized state to be injected into the forming mold A through theinlet port 81 by means of the injection machine S at the airtightnessreleased position O₃ to which the movable mold part 4 has been moved bymeans of the mold operating mechanism. At this time, the forming space Ris permitted to communicate with an ambient atmosphere through thecommunication holes 82, resulting in being released from pressure, sothat expansion force due to vaporization of moisture contained in theresin leads to formation of the biodegradable resin foam. Immediatelyafter the foaming, actuation of the mold operating mechanism permits themovable mold part 4 to be rapidly moved to the pressing position O₅ toreduce a volume of the forming space R, so that formation of thebiodegradable resin foam may be carried out while keeping the productcompressed. Thus, it will be noted that such injection of thebiodegradable resin into the forming space R at the airtightnessreleased position O₃ exhibits the same function and advantage asdescribed above.

The above-described construction of the illustrated embodiment may beincorporated in the apparatus shown in FIG. 35. Thus, movement of themovable mold part 4 of the forming mold A to the pressing position O₅ bymeans of the mold operating mechanism upon the foaming causes a decreasein volume of the forming space R, resulting in the biodegradable resinfoam B being provided while compressed. After the foam product B iscooled, to thereby be solidified, the movable mold part 4 is moved tothe released position O₁ by means of the mold operating mechanism,followed by removal of the resin foam B from the forming mold A. Suchconstruction exhibits the same function and advantage as describedabove.

As can be seen from the foregoing, the biodegradable resin foam of thepresent invention comprises a combination of the main biodegradableresin ingredient or first biodegradable resin ingredient having amelting point of 100° C. or more and the low-melting biodegradable resiningredient or second biodegradable resin ingredient having a meltingpoint of 100° C. or less. Thus, in the resin foam, the secondbiodegradable resin ingredient is kept from being immediatelysolidified, to thereby function as an adhesive with respect to the firstbiodegradable resin ingredient. Thus, even when any cavity and/or voidare An generated in the foamed biodegradable resin, cells of the foamedresin are permitted to adhere to each other, resulting in thebiodegradable resin foam being provided with satisfactory quality.

In particular, when the second biodegradable resin ingredient isselected from the group consisting of polycaprolactone and a materialcontaining polycaprolactone, the function of the second biodegradableresin ingredient as an adhesive is significantly enhanced. Also, whenthe biodegradable resin has polyhydric alcohols and derivatives thereofadded thereto, moisture in the biodegradable resin is increased inboiling point, resulting in functioning also as a plasticizer, so thatcells of the foamed biodegradable resin are rendered dense and uniform.

In the method of the present invention, the biodegradable resinfluidized due to an increase in temperature thereof is rapidly releasedfrom a heated and pressurized environment in the cylinder and extrudedinto the air-permeable forming mold, to thereby be formed into apredetermined configuration. Thus, moisture contained in thebiodegradable resin is increased in boiling point under pressure,resulting in being in the form of liquid in the cylinder, so thatreleasing of the resin from the heated and pressurized environment inthe cylinder causes the moisture to be instantaneously vaporized,leading to foaming of the resin. The resultant water vapor is outwardlydischarged through the air-permeable forming mold, to thereby beprevented from adhering to the formed resin foam.

The atmosphere in which the forming mold is placed may be kept decreasedin pressure or ventilated after extrusion of the fluidized biodegradableresin into the mold is started or since a stage before the extrusion isstarted. This prevents moisture from remaining in the form of steam inthe forming mold or being condensed on a surface of the biodegradableresin foam due to a decrease in temperature after vaporization andexpansion of the moisture, resulting in the resin foam being providedwith satisfactory uniformity.

In the method of the present invention, extrusion of the fluidizedbiodegradable resin into the mold may be carried out while placing thenozzle arranged with respect to the narrowed opening in the depths ofthe forming mold at the time when operation of the nozzle is started andretracting the nozzle relative to the forming mold during extrusion ofthe biodegradable resin. Such construction permits the biodegradableresin to be charged in the forming mold in order from the side of thedepths of the mold, resulting in a different between a timing at whichthe resin is spread throughout the forming mold and a timing of foamingof the resin being minimized or substantially eliminated, to therebysubstantially prevent cells of the foamed biodegradable resin from beingcollapsed.

In the method of the present invention, extrusion of the fluidizedbiodegradable resin into the forming mold may be carried out whilekeeping an atmosphere in the forming mold pressurized during theextrusion and a pressure in the atmosphere in the forming mold may berapidly reduced after completion of the extrusion.

In the method of the present invention, extrusion of the fluidizedbiodegradable resin into the forming mold may be carried out byinjecting the biodegradable resin into the forming mold while keepingthe resin atomized. This permits not only the biodegradable resin-to bespread throughout the forming mold but the atomized biodegradable resinto be effectively foamed, followed by integration of cells of the foamedresin substantially without being collapsed, to thereby provide thebiodegradable resin foam with increased uniformity.

In the method of the present invention, the biodegradable resin startingmaterial may comprise the biodegradable resin, moisture and waterrepellent material. The starting material of such composition ensuresdesired foaming of the biodegradable resin and permits it to be finelyand uniformly foamed.

Also, the water repellent material may comprise a material which is notfully evaporated when the biodegradable resin is released from theheated and pressurized environment. Such a material includes a naturalfatty acid polymer. Use of the polymer as the water repellent materialpermits it to cover cells of the foamed biodegradable resin to provideit with water repellent properties, to thereby prevent the cells frombeing collapsed due to contact with water.

In the method of the present invention, the step of forming the foamedbiodegradable resin into a shape depending on a configuration of theforming mold may be carried out by forming the whole biodegradable resininto an integrated configuration. This permits the biodegradable resinfoam to be formed into a relative large volume or any desiredconfiguration.

The apparatus of the present invention is so constructed that thepressure adjusting chamber is constructed in an openable and sealablemanner, the air-permeable forming mold is arranged in the pressureadjusting chamber, the pressure reducing tank is connected to thepressure adjusting chamber to rapidly reduce a pressure in the pressureadjusting chamber, and the injection machine is arranged injecting, intothe forming mold, fluidized biodegradable resin placed in a heated andpressurized environment and having moisture trapped therein. Suchconstruction of the apparatus permits the pressure reducing tank tocommunicate with the pressure adjusting chamber after injection of theresin into the forming mold, so that water vapor in the forming mold maybe effectively outwardly discharged, to thereby eliminate retention ofmoisture in the forming mold. Thus, the apparatus of the presentinvention provides the biodegradable resin foam with a desiredconfiguration and uniform quality.

In the apparatus of the present invention, the pressure adjustingchamber may have the evacuation valve connected thereto. Thus, when thepressure adjusting chamber is rendered open to an ambient atmosphere inthe course of injection of the biodegradable resin, resistance toinjection of the resin into the forming mold arranged in the chamber isreduced because the forming mold is air-permeable, so that the injectionmay be facilitated. Thus, the injection machine is prevented from beinglarge-sized.

In the apparatus of the present invention, the pressure adjustingchamber may have a compressor connected thereto. Such constructionpermits injection of the biodegradable resin into the forming mold bymeans of the injection is carried out while keeping moisture positivelytrapped in the resin because actuation of the compressor causes thepressure adjusting chamber to be pressurized. Then, operation of theevacuation valve results in the pressure adjusting chamber beingreleased from pressurization, leading to a decrease in injectionresistance, so that the biodegradable resin may be spread throughout theforming mold.

In the apparatus of the present invention, the pressure adjustingchamber may have a pressurizing tank connected thereto. Thus, thepressure adjusting chamber is rapidly pressurized at an appropriatetiming when the biodegradable resin is to be injected into the formingmold. .

In the apparatus of the present invention, the valve controller may bearranged so as to control operation of the pressure reducing valve,operation of the evacuation valve and actuation of the compressor, sothat the pressure adjusting chamber may be controlled to pressurization,evacuation or pressure reduction in association with a timing ofinjection of the biodegradable resin into the forming mold by means ofthe injection machine.

In the apparatus of the present invention, the valve controller may bearranged so as to control operation of the pressure reducing valve,operation of the evacuation valve and actuation of the pressurizingvalve, so that the pressure adjusting chamber may be controlled topressurization, evacuation or pressure reduction in association with atiming of the injection.

In the apparatus of the present invention, the valve controller may bearranged so as to control operation of each of the pressure reducingvalve and evacuation valve, so that the pressure adjusting chamber maybe controlled to evacuation or pressure reduction in association with atiming of the injection.

In the apparatus of the present invention, the valve controller may bearranged so as to control operation of each of the pressure reducingvalve and pressurizing valve, so that the pressure adjusting chamber maybe controlled to pressurization or pressure reduction in associationwith a timing of the injection.

While preferred embodiments of the invention have been described with acertain degree of particularity with reference to the drawings, obviousmodifications and variations are possible in light of the aboveteachings. It is therefore to be understood that within the scope of theappended claims, the invention may be practiced otherwise than asspecifically described.

What is claimed is:
 1. A biodegradable resin foam made of biodegradableresin by expansion force due to vaporization of moisture caused byrapidly releasing fluidized biodegradable resin which is in a heatedand-pressurized environment and in which moisture is trapped; saidbiodegradable resin comprising a combination of a first biodegradableresin ingredient having a melting point of 100° C. or more and a secondbiodegradable resin ingredient having a melting point of 100° C. orless.
 2. A biodegradable resin foam as defined in claim 1, wherein saidsecond biodegradable resin ingredient is selected from the groupconsisting of polycaprolactone and a material containingpolycaprolactone.
 3. A biodegradable resin foam as defined in claim 1,wherein said biodegradable resin has a substance selected from the groupconsisting of polyhydric alcohols and derivatives thereof added thereto.4. A biodegradable resin foam as defined in claim 2, wherein saidbiodegradable resin has a substance selected from the group consistingof polyhydric alcohols and derivatives thereof added thereto.
 5. Thebiodegradable resin foam of claim 1, comprising foam cells having wallsbonded to each other by said second biodegradable resin ingredient.
 6. Abiodegradable resin foam made by the process of expanding abiodegradable resin by rapidly releasing fluidized biodegradable resinthat is in a heated and pressurized environment with moisture trappedtherein so that the moisture is vaporized to cause an expansion force,the biodegradable resin comprising a combination of a firstbiodegradable resin ingredient having a melting point of 100 degrees C.or more and a second biodegradable resin ingredient having a meltingpoint of 100 degrees C. or less.
 7. The biodegradable resin foam ofclaim 6, wherein said second biodegradable resin ingredient is selectedfrom the group consisting of polycaprolactone and a material containingpolycaprolactone.
 8. The biodegradable resin foam of claim 7 whereinsaid biodegradable resin further comprises a substance selected from thegroup consisting of polyhydric alcohols and derivatives thereof.
 9. Thebiodegradable resin foam of claim 6 wherein said biodegradable resinfurther comprises a substance selected from the group consisting ofpolyhydric alcohols and derivatives thereof.